Dread Necromancer
A Dread Necromancer is a necromancer who's more of a necromancer than other necromancers. In fact other necromancers wish they were as much of a necromancer as a dread necromancer. They also sometimes wear dreads.
I dread to think that this is all anyone could come up with for this class...
What it does
Originally from the Heroes of Horror 3rd Edition D&D supplement, it is the best attempt at creating an Arcane caster that specialises in Undeath.
This is no bad thing, because proper necromancy is usually the domain of Death Cleric who usually get the same spells (like Animate Dead) earlier, or are simply more effective due to the ability to channel positive/negative energy.
The class itself plays like a Sorcerer albeit with a preset selection of spells that you can cast without preparation. Just don't expect to cause stupid amounts of direct damage as other arcane casters do since you'll never get access to most of the flashy spells and are stuck almost exclusively with Necromantic Magic. Though you can start drawing divine spells from the cleric list later in your career. You can even cast spells in light armour without suffering spell failure chance.
If you were a Sorcerer who wanted to heavily focus on necromancy this would be the better way to go anyway, unless you were optimising your build around your specific selection of spells or hoping to obtaining a particular prestige class (*cough* What all these specialized Sorcerers try to access: Rainbow Servant *cough*).
But the real draws to this class though are the class features it grants and is in fact one of the 3rd edition classes that really benefits from taking it all the way to the end, rather than jumping ship and multiclassing. So if all you want/need is a few levels of generic arcane casting from somewhere, you're better served with a different class.
First, you can Rebuke/Command Undead as a Cleric does of your level.
You also get a whole bunch of neat supernatural abilities that scale as you level up; one example is the ability to apply negative energy damage as a touch attack every turn (with no usage limit) which also heals friendly undead. Another is an aura of fear which emanates from yourself which you can raise and lower at will.
As you level up, your ability to generate your own minions becomes really useful too: Any created undead get better, in that they get persistent stat bonuses to STR & DEX and you can summon more and more of them. You can also eventually get your own Improved Familiar (Quasit, Imp, Varghouille or Ghastly Visage) which can channel your class abilities for you.
Finally, your class progression always leads you to become a Lich, gradually providing you with steadily improving immunities to damage, mental effects and negative energy spells. Making you fully undead at level 20. Yes, other spellcasting classes could become Liches at earlier levels, but at least a Dread Necromancer never has to do the legwork.