Tarpit

In Warhammer terminology (both Warhammer Fantasy and 40k), a Tarpit is a big blob of expendable and/or durable infantry intended to be a giant pain in the ass and functionally a living wall designed to slow enemies down and keep foes tied up by either flanking/assaulting them, or act as a wall of dakka. Ideally capable of being placed in cover, almost every faction in both games is capable of fielding some unit or another that serves this purpose. Some are especially good at it or are built on the concept, whilst others are simply mediocre at it.

Warhammer Fantasy

In Warhammer Fantasy, the game is much more about punchan' games supported by magic and ranged options. As such, rather than 40k where tarpits serve to stop an assault, almost all armies in the game use a "hammer and anvil" approach where you first have a giant block of troops designed to get into Close Combat and stay there, then one or more very high-damage (and usually either point-expensive or very flimsy) options designed to hit what's stuck in combat from the flank. That is why Movement and table tactics in general are much more important in Warhammer Fantasy; cover saves you from arrows and bullets, but a cannonball will go straight through the trees and you usually want to take your time playing a game of chicken to redirect your opponent to be fighting with their backs to a dangerous swamp, or with a wall on your left so the enemy can't flank you from that side. In addition, there is a subcategory of tarpit called "redirectors" who serve to be an obstacle between your opponent's offensive troops and your sides. For example, by putting ten Spearmen standing sideways and in single rank on the side of your horde of 5 ranks of ten Spearmen then you gain one turn between the opponent charging the side of that unit with cavalry. You also change the direction their Charge comes from, which can fuck over cavalry (this is considered a current weakness of the rules, and there are rumors there will be changes to redirectors in the 9th edition).

Beastmen

• Beastmen Ungors are cheap as dirt and have shit stats, but they can be taken en masse to provide a useful meat-shield.

Bretonnia

• Brettonian Men-at-Arms are cheap, have decent armor, and easy to acquire in bulk. A surprisingly durable tarpit.

• Grail Reliquae and Battle Pilgrims are way more expensive than Men at arms and aren't any better at killing things for it. On a plus, the Reliquae provides a 4+ armor save, they automatically receive Blessing of the Lady (6+/5+ ward save) and they are stubborn.

Daemons of Chaos

• Plaguebearers are a bit different from most other tarpit units, instead of relying on massive numbers, they rely on being nigh-unkillable. With a toughness of 4, a 5+ regeneration save and enemies receiving -1 to hit while in close combat with the plaguebearers, it is an exceptionally tough nut to crack. On top of that delicious, pus-leaking, bile-streaming jolly group, they have strength 4 and poisoned attacks, so they pack quite a meaty punch as well.

Dark Elves

• Bleakswords: Your basic swordsmen with a sword and shield. The parry save is useful in melee and they're really fast with a good weapon skill so they'll deal some damage while tarpiting your enemy.
• Black Guard: A hard hitting unit. Unlike most tarpits their rather easy to damage and are rather expensive at 15 points but they'll never break. They're high initiative and ASF will mean that they will deal a lot of damage to whatever they catch.
• Sisters of Slaughter: The defense to the Witch Elves offense. A 4++ ward save in close combat is massive.

Dwarfs

Dwarfs are a very slow army, and in most cases need the enemy to come with them. Luckily they fight like Napoleonic era armies, fielding gunlines with ample artillery support. But they rely on keeping things out of the face of those models, or in making openings for the killy infantry options.

• Dwarf Warriors - Cheap as far as Dwarf models go, 200 points gets you a good 20-man block to stop other infantry. Anything killy will shred through them, and cavalry will trample them like Mario jumping on Goombas. Generally, they aren't worth what it takes to make them more durable since they're just there to stop what's in their path, like most examples on this page.
• Iron Breaker - Super durable. While your Dwarf Warriors make up a roadblock, Iron Breakers are a true tarpit; whatever gets into combat with them is probably STAYING in combat with them. Almost twice the cost of your warriors, and nearly 8 times as better. If you're using Iron Breakers and Warriors at the same time, your Warriors may be large redirectors for your true unbending and crotchety Iron Breaker horde.

High Elves

High Elves are a lower population army, and somewhat fragile. They can use magic to great effect to increase their chances, but generally rely on killing the opponent quickly before that becomes an issue.

• Spearmen - Come at 9 points a pop, and are pretty damn easy to kill. They can attack in one more rank than most roadblocks because they're glorious Asur, and aren't terrible at killing. They can also carry a cheap magic flag, but most of those in their cost allowance are pretty bad so this isn't generally taken advantage of. They come to the fight with shields, but they gain no parry safe, since they are fighting with spears. They're the cheapest possible horde option for High Elves, and thus the primary tarpit option. Although their survivability can be boosted in various ways they're left to their own destiny more often than not, but the fact that the high price of most elf options means High Elf players are more likely than most to consider throwing some defensive magic from the Lore of Life or the Lore of Light on them.
• Silver Helms - The cavalry version of Spearmen. Come much more expensive at 23 points a pop with shields, and have a similar statline, but on the charge do a great deal of damage and are highly mobile. In a full cavalry list they will take the place of the Spearmen as a tarpit for the more offensive options like Dragon Princes or White Lion Chariots to flank the opponent, and with their lower numbers are more likely to have a combat character in their ranks or receive defensive magic than their peasant kin.
• Ellyrian Reavers - Fast light cavalry, can take bows and/or spears. More expensive than Spearmen, less expensive than Helms, and with the statline as Spearmen barring the fact they're on horseback. A unit of five can make a pretty decent redirector, as the only other option for that is a Great Eagle which costs as much and is easier to kill on top of eating points from the rare category.
• Phoenix Guard - Elves so badass they look Chaos Gods in the eyes and just sneer. A special choice, ringing in at 16 points a pop. The defensive godlings of the game, they are Immune to Psychology and Cause Fear due to how unnervingly unafraid of you they are. Heavily armored, almost max LD on top of that fearlessness, three ranks of attacks, S4, and a 4+ Ward Save. Factor in the buffs they can have (bump up to a 3+ Ward, Regeneration, and Toughness up the yin-yang) and you have something that just won't fucking die. Oh, then you decide you don't need friends and put Banner of the World Dragon on them, making them untouchable by Magic damage (the ENTIRE Daemon army has Magic Attacks, so not even Slaanesh himself could touch them at this point). So not only are they durable, but also killy on top of it. You field Phoenix Guard when you just don't want to budge.

Lizardmen

• Saurus Warriors are tough and hard-hitting ( LD8 with the coldblooded rule, T4, 2 S4 attacks each, and they gain bonus attacks for every 6 to hit they score): Saurus can realistically tarpit anything short of Dragon Ogres, especially if taken in good numbers or backed with some buff from a nearby Slann. Their role is usually to serve as an anvil while some kind of big, scary dinosaur like a Stegadon prepares to flank charge, but given their offensive presence they are also good in the role of the hammer.

• Skink Cohorts are in many ways similar to goblin hordes: huge chunks of cheap, spammable infantry, coming at 7 points a pop, with some dirty tricks in the form of poisoned javelins and poisoned hand weapons which will probably net you some kills given their good initiative of 5 and the possibility to stand and shot. What sets them apart from ungors, goblins and clanrats is that you can buy kroxigors in the second rank of the unit (they can still use their 3 attacks from there, but can also be targeted in meelee), which will give skinks better discipline, fear, and overall better survivability, with the downside of being rather pricey and requiring 8 skinks for every kroxigor you wish to field.

• Skinks Skirmishers are cheap, spammable, mobile (they move 6, have marsh and river strider, and gain cover while in water) and with their poisoned ranged weapons, they can be an irritating thorn in your opponent's side, acting as charge redirectors and forcing your opponents to deal with them. They can force your opponents to chose one among two bad choices, either wasting important resources on a weak unit while letting your saurus warriors and dinosaurs advance unscathed, or lose valuable troops or war machines from lucky poisoned shots. Just remember, they are not skavenslaves, since they can actually kill things rather then being only cheap meat shields, so use them carefully and intelligently to get the most from them.

• Jungle Swarms are... swarms. So they're kinda meh in everything they do. They can be good redirectors, but you are usually better off with skinks. Swarms' ability of having all your other troops fighting in the same meelee as them gain poisoned attacks is nice though.

• Temple Guards are NOT tarpits. They are a bunch of murderous alien-dinosaur-people that can and will destroy ANYTHING you send them at. TG are tougher then Warriors, hit even harder, and will NEVER run away. Take'em in packs of 20/30 soldiers, set a flank charge, and watch the meatgrinder get started.

Ogre Kingdoms

• Gnoblars: The cheapest models in an army of elitist brutes. 10 of these can be taken at the cost of a single Ogre and can be further upgraded to trappers in order to act as a screening unit by making everything take difficult terrain tests when charging them.

• Ogres: The basic unit of an Ogre Kingdoms army and damn tough. With Toughness 4 and three wounds they can whether attacks with ease. Get Ironfists to upgrade their 6+ to a 5+ and they'll weather hits like a champ.

Orcs & Goblins

• Orc Boyz: Toughness 4 infantry at 6 points a model. You can even swap their role as tarpit to killer thanks to being S4 on the charge.

• Goblins: Cheap at 3 points. They'll have a ton of wounds to each unit.

• Night Goblin: They may seem inferior than normal Goblins due to having 1 less leadership. They become great when you take netters which allow them to reduce the strength of attacks against them.

• Snotlings: A horde of T 2 wound 5 unbreakable units. Plonk them on an objective and they'll never leave it.

Skaven

Army full of tarpits. Rival Tomb Kings and Vampire Counts on the title of being the best.

• Skavenslaves - one of the most awesome tarpits in the game. First of all, they are cheap. And by that I mean 2pts/model. Since they have hand weapons, you can give them shields, making them 1/3 more durable (even though 6+ armor won't stop anything, 6+ parry save is kinda nice). But that's not the best part. They "explode" (or, rather, die in murderous rage) when they break, hitting all nearby units. So, even if they fail, they take some enemies with them. Which is also nice, but still not the best part. The best part is - no one cares about the slaves, so Skaven are allowed to shoot at close combat involving Slaves. Shooting an elite enemy squad to bits while it is locked in combat with dirt-cheap slaves? Priceless. Sure, some slaves will die to randomized shots, but given their numbers, no one cares.

• Clanrats - twice the cost of slaves, can't be shot at by allies and don't explode. However, they have higher WS and light armor, making them somewhat more durable. Better take Slaves as tarpit and give Clanrats spears.

• Giant Rats - kidna meh. Slaves are cheaper and more effective. And you can shoot at them.

• Rat Swarms - kidna meh too. Slaves are cheaper and more effective too. And you can shoot at them too. Still, you sometimes get some free Rat Swarms from a dead Abomination.

• Plague Monk Horde with Plague Furnace - not really a tarpit, since it is very killy, but it still will tie an enemy down and destroy him through heavy attrition.

• Gutter Runners with Snare-Nets - an uncommon and costly option, but their fine WS, 6+/6++ and the nets reducing enemy attacks by 1 (to a minimum of 1), Gutter Runners can hold low-strength dual-wielders (Plague Monks, Witch Elves, Dryads, Free Companies, Corsairs, you name it) pretty well. Just keep a general nearby - Skaven are cowardly.

The Empire

• Spearmen / Halbardiers: cheapest empire models, although there is'nt much more to say about them. Spearmen get the usual extra rank, halbardiers the +1S. Both are 2H weapons so shields are only useful against shooting attacks.

• Swordmen: these cost a tiny bit more than the spearmen & haldbardiers but get +1 WS and a shield, meaning both armor save and parry save.

• Greatswords: the elite of Empire infantery: full plate armor, stubborn and room for a magic banner. Their great weapons make they can dish out a decent amount of damage as well. These come at roughly twice the cost of the above 3.

• Flagellant Warband: unbreakable, frenzy, and if you allow some of them to cut their own hearts out as an offering to Sigmar the remaining models can get some nice buffs. No armor however, and the buffs are mainly on the offensive side of the spectrum. Not the very definition of a tarpit but they'll keep their opponent busy.

Tomb Kings

• Skeleton Warriors: fear is nice, unbreakable is better (albeit it comes with unstable), and their low price tag means you can field hordes upon hordes of 50+ skellies without crippling your army size, which is what you should do if you're not going for the Bone Train Army (aka chariots spam). You can raise d3+1 models with every augment you cast on them from the Lore of Nehekara, allowing skeletons to sustain extended periods of combat and tarpit units way pricier than them. Having a Tomb Prince tagging along with them will instantly send their pathetic WS 2 straight through the roof, leading to situations like chaos warriors struggling to hit them: this could not be game changing but surely is hilarious.

• Tomb Guard: beefed up skeletons that are a clear step above your troop choices but also cost 11 points each (13 with halberds, and you should probably give them halberds because 1, you want them to be very killy, and 2, they're going to be a huge point sink anyway so go ahead and load'em with anything you've got). Packing killing blow on top of their improved statline means they are your Hammerers/Temple Guard/Bloodletters equivalent and so they're better used as a huge deathstar unit rather than to tie things up, especially when you can put a Tomb King in their first rank to have them all gain WS7.

• Scarab Swarm: it's a swarm, what do you expect from it? But Entombed Beneath The Sand gives it good times ruining your opponent's plans by popping everywhere on the battlefield redirecting charges. Still, a mediocre option when you can EBTS the like of Necropolis Knights, Tomb Scorpions and Sepulchral Stalkers.

• Khemrian Warsphinx: Hell yes T8 W5 giant stone kitty with a 5+ and regeneration from nearby necrotetcs. While not a tarpit by any means, its awesome toughness means anything short of cannons or great weapons-wielding critters as a Shaggot or blocks of Kroxigors will struggle to get through (and you can still heal the sphinx as you do with skeletons, albeit only one wound per augment) so in a pinch it can block a bunch of low-strength mooks like Corsairs or Goblin for a long time while cleaving through them.

Vampire Counts

The best tarpit army in Warhammer Fantasy. Capable of using magic buffs to make their tarpits decent and killy, and even more than that. Oh, and they can raise them by spamming cheap spells back to full strength, in some games doubling the number of models on the field by the time they reach Close Combat. They can create new units entirely with higher level spells as well. But if the army General dies, models begin to suffer Crumble and the tarpits usually have low Leadership, meaning they're the first to go unless they have a character with them to keep them moving; after that, a character may attempt to take over as the General and save the army. Almost all VC models (all actually, except the two living Necromancer options) are Undead and thus cause Fear. This is a VERY good thing for them.

• Zombies - Almost the cheapest models in the game at 3 points each (Skavenslaves are cheaper, 2pts each). So weak that it's damn near impossible for them to kill most things, even other tarpits. They actually come with an ability amplifying the number of models raised with magic.
• Skeleton Warriors - Cost more points at five a pop and a bit harder to raise, but are more survivable and a pinch more killy. Can be outfitted with spears instead of their shield and hand weapon, but since it doesn't particularly make them much better and they lose the Parry bonus from their shields it's generally not worth considering. Only Necromancers can increase the number of Skeleton Warriors above what you start with, and even then only ONE Necromancer in your army can with a point upgrade. They can also take a magic flag, and there's a nifty one in their price range that makes enemies far more likely to run screaming from them.
• Crypt Ghouls - The "liveliest" of the core options. While they fulfill the same role as a tarpit, they're the most killy option. While they lose out on the shield and light armor of the Skeleton Warriors, they do come with an extra point of Toughness. They have double the attacks, and any roll of 6 causes an automatic Wound because they have Poisoned Attacks. Sadly, they come at 10 points a pop and in addition they cannot summon more into the game by healing them, only restore casualties. They can tie up enemies in combat and deal fuckhuge amounts of damage on par with the Special options of many other armies.
• Dire Wolves - The "cavalry" equivalent to the Skeleton Warriors. They are a bit more killy, especially on the Charge. Most players use them as redirectors for their tarpit horde, or as a block of warmachine hunters. They aren't bad when going after a juicy flank stake either (*double rimshot). They're not great as a tarpit horde however, because they cost 8 points each. Only Vampires can summon them beyond their starting value with a point upgrade.
• Spirit Hosts - A swarm of three ghosts. Ghosts can only be hit by Magic Attacks, or crumble from Combat Resolution but you can take them in units up to a maximum of ten swarms of three. It's very possible to get them to haunt the face of a monster and literally tie it up the ENTIRE game, doing mosquito bite attacks until they manage to kill it. As such, these are the god mode redirectors and oftentimes tarpits of the game.
• Grave Guard - The special category version of Skeleton Warriors. Much better at dealing damage, and more durable as well. While they usually serve in the former role a large unit being healed can tie up enemies for a whole game while whittling them down.
• Black Knights - Grave Guard in cavalry form. Expensive for points, and thus outside large point games are unlikely to see action as a tarpit. But they CAN be used as a redirector, switching to the hammer role once the horde gets into Close Combat.
• Crypt Horrors - The special version of Ghouls. They come with Regeneration 5+ allowing them to survive Wounding attacks unscathed. This can be further bumped up with a Mortis Engine on hand improving their Regeneration score. If you want to spend the points on them and keep them healed, these can be almost the Phoenix Guard of this army.
• Bat Swarm - Technically the use of the Bat Swarm is to go into the flank of the enemy, granting them Always Strikes Last which can greatly improve a tarpit of Ghouls and Horrors by allowing to get their shots in before taking any. But until they move forward in that role, they're usually found on the side of a unit serving as a redirector.

Warriors of Chaos

Tarpits in a Warriors of Chaos army can either be Tzeentch or Nurgle aligned. Nurgle will make them tougher overall by making all attacks less likely to hit which is useful in general. Tzeentch will grant the unit a 6++ ward save that goes to 5++ in melee when equipped with shields. Quite helpful if your opponent brings a lot of stuff that ignores armor saves or even turns them against you.

• Chaos Marauders: The cheapest unit in your army at 6 points a model and more skilled in combat than most other races core and even some of their special choices.
• Chaos Warriors: These are the cheese of the Warriors of Chaos. With a 4+ armor save a lot of attacks will bounce off their armor and this goes to 3+ with shields.

Wood Elves

• Eternal Guard - superb tarpit, being Core, Stubborn spearmen with 5+ save and WS5. They can even deal some damage in return with their AP spears.

• Dryads and Tree Kin can be used as tarpits (which their high T may suggest), but their high cost and poor saves make them sub-optimal for that, when compared to Eternal Guard. Still, it can work. Also, the treeman. It's basically his only job with him being tough as hell and stubborn Ld 9.

• War Dancers - though normally as hard as wet tissue paper, War Dancers can serve as temporary tarpits with their 3++ for 1 turn. May be very well enough to hold an enemy unit for flank charge.

Warhammer 40k

Imperial Guard

• Conscript Platoon - 20+ Models for dirt cheap. Do the math. Get all 50 for 150 points and stick a 25pt Priest w/Autogun with them so they will never, ever go away. Hell with Hatred and possible re-rolls to wound they might inconceivably actually kill something in cc.
• Regular Guardsmen - They're 2 point highers than conscripts. If you want some guys who can fight a little better and stand as fuckheug blob, these are your guys. Terrifyingly shooty and you can actually arm them to be useful in assault. If your dice rolls are lucky, you should usually take lots of guardsmen and tanks.
• Chimera APC - Cheap as shit and easy to get for some beefy armor that will tend to stick around all game long. Once they're done transporting, feel free to have your entire force group of Chimeras gang up and proceed to start roving in angry packs like a gang of 1920s Irish immigrants dealing with abuses by the police.
• Taking a Dark Angels allied detachment with Azrael will give a 50-man guard platoon 4++ saves and furious charge, ensuring that nothing short of top-tier firepower will get rid of them. Throw in a priest to get a rerollable 4++, or slightly better than storm shield saves.

Chaos Daemons

• Nurglings - Gets into close-combat and keeps enemies tied up for half a game or longer.

Tau

• Kroot Carnivores - Inexpensive infiltrating models at 6 points base. Hell of an area denial unit that can frustrate anyone trying to deepstrike that Dreadnought near your battlesuit formation.
• Gue'vesa Auxillaries - Even less expensive and can't infiltrate but shooty and with decent wargear options.

Tyranids

• Ripper Swarm - Vulnerable to Instant Death, blast templates, and they die without synapse, but will tie foes up for round after round if they get close for a low price.
• Gaunts - Cheap and effective mass unit. When used with Tervigons they can stay around forever and ever and ever.

Orks

• Nearly every type of cheap yet numerous Ork Boy squad (Sluggas, shootas, et cetera). Sluggas works best at tying up enemy units overall though, a mob with 4 S4 attacks and near marine toughness will keep all but the 'ardest and killiest units from quickly getting rid of them. These guys are also your main troop choice as well, and will drown your enemies in close combat attacks as well as bodies.
• Gretchin - Dies like bitches to nearly everything, but numerous, can hold objectives, dirt-cheap, and can actually shoot better than most Ork boyz (so can anything with their eyes open (with less dakka)). Their prime use is pretty much to act as a walking meatshield in front of your sluggas so they won't go down on the initial charge on your opponents formidable gunline... Yo dawg, we heard you like tarpits, so we put a tarpit on yo' tarpit so you can tarpit while you tarpit... well, unless your opponent is packing a retarded amount of arty, which kinda renders this no more than a minor inconvenience for them.
• Take Mad Dok Grotsnik and for a bump in cost make the Tarpit unit cyborked, giving that large annoying tarpit unit 5+ invuls. It costs a bit, but when your models are this cheap its worth it just to see that smug smirk die when that IG player's Leman Russ tank kills only 6 gretchin, or a Defiler fails to kill a single Boy in close combat before the Powerklaw tears it in half.

Necrons

• Scarab Swarm - Vulnerable to instant death/blast temps, but cheap for 30 wounds in a squad. They eat tanks and dreads like Abaddon eats people, so they tend to draw a lot of firepower from your other units.
• Warriors - When DON'T you have a metric fuckton of warriors while playing as 'cronz? Very good if paired with the right formations and/or a Necron Lord with a resurrection Orb and is capable of Gauss-glancing any vehicle into dust in one round of shooting. A lord with res orb and a nearby ghost ark will make sure that these dudes don't go down any time soon.

Eldar

• Guardian squad - They're the cheapest and most numerous infantry squad you could field in an Eldar army and attaching a warlock with either embolden or conceal could allow them to do their jobs better at a low point cost, though honestly Eldar really shouldn't be tarpitting unless you're in a desperate situation. They're better off shooting than knifing someone to death though, unless you use Storm Guardians.

• Wraithblades aren't cheap but they have the T of a Riptide, MEQ armour saves and can take a 4++ for free. They also don't run away and hit back with high S power weapons. A big squad will hold up anything without lots of High S or Poisoned attacks for ever and deal back alot of damage.

• Eldar don't really have much in the way of Tarpitting. Whilst the Wraithblades can "tarpit", it's not really tarpitting as much as a general cc unit. Instead ally them with Guardsmen and take fuckhueg blobs of conscripts.

Dark Eldar

• Wyches - They're a mildly effective close combat unit in their own right, but loading them up with Shardnets reduces enemy attacks, and they all get an invulnerable save. A great option for swamping Terminators and the like, and can actually beat a softened up terminator squad with a couple of lucky rolls due to the cost:attacks ratio between wyches and terminators (though this isn't nearly as effective due to 6th edition power weapon rules).
• Grotesques - While not really a tarpit, they're mad tough, especially if led by a Haemonculus, and can tie up MEQ and weaker infantry units with ease; they could probably tie them up for at least half the game or kill them outright.

Space Marines

• Scouts - They infiltrate, they can pump a good amount of dakka downrange, and about the cheapest unit you can field in an SM army.
• Rhino Transports - Once your Rhino already unloaded its troops, it functions as an annoying well-armored blockade/brick of cover that pretty much prevents your enemy from properly assaulting or targeting their intended target, park them in front of a squad about to be charge or taken out by a heavy weapons team - voila, instant cover. And to boot, it's cheap and still has a Storm Bolter to threaten a few weedy gits.

Space Wolves

• Fenrisian Wolves - While they're fast attack instead of troops, they're cheap, comes with a handy 6+ save and aren't that bad in melee.

Grey Knights

• Castellan Crowe - He would stick in combat like forever with his rerollable 2+/3++ save, while burning shit to death with his bare mind.

Chaos Space Marines

• Cultists - If you've played any army requiring mass infantry formations, you know what to do. Give them the Icon of Nurgle. Laugh manically.
• Plague Marines - Papa Nurgle's good ol' T5/FnP plagues, these guys will never fucking die until someone whips out high-powered anti-armor weaponry. Plonk 7 of them and watch them weather out phase after phase of attacks. Seriously, seeing Plagues tank 30+ Orks with only a single casualty across three rounds is far from unheard of.
• Thousand Sons - Expensive, much as the Plague Marines are, but definitely a worthy entry. They aren't quite as tough to kill against small arms fire as Plagues, but they'll survive heavier firepower with ease and will basically laugh off power weapons, which Plague Marines won't. They also hose out a lot more dakka than a Plague squad. Watching an enemy nearly shit themselves after dropping a Demolisher Cannon pieplate on them only for their 4+ invuln save to shrug it off is hilarious, and they're likely to keep anti-tarpit SCs like Lelith Hesperax or Typhus away because of the Force Weapon used by the Sorcerer.
• Rhinos - OUR ENEMIES HIDE BEHIND METAL BAWKSES! THE COWARDS! THE FOOLS! We... We should hide behind our own metal boxes... Has exactly the same advantages as the block of cover used by the loyalist bastards, with a Havoc and some other fun stuff thrown in.
• Plague Zombies - Now troop choices in CSM armies by taking Typhus as a HQ. Take 35. They're both fearless and feel no pain and a massive pain in the arse for anyone planning on shooting anything.

Sisters of Battle

• Ecclesiarchy Battle Conclave - Storm shields for 15 points? Yes please. Don't expect them to survive against TEQs for more than 2 turns though.
• Blobs of 20 sister of battle with flamers and priest. Fearless, hainous, rerollable 3+ save wall of flame for the same price as marinescouts. The true meaning of tarpit

Lost and the Damned

• Mutants - This unit basically exists for this purpose.
• Plague Zombies - World's best tarpit. Cheap as Conscripts, and slow moving, but has feel no pain and fuckhuge numbers. Just don't let the tau see them or they vaporize.
• Traitors - See also: Guardsmen.