Soulknife
The lightsaber of Star Wars fame and all weapons like it are universally accepted as one of the most awesome weapons in fiction. And the ability to create a lightsaber with your mind sounds double awesome. Hence, one day after smoking an entire market's worth of opium, someone at Wizards of the Coast thought it was a good idea to create the Soulknife for the Expanded Psionics Handbook of 3.5e Dungeons and Dragons. Unfortuately, like many before it in third edition, this did not turn out all too well...
KNIFE MIND ATTACK
The main feature of the Soulknife is its primary weapon and namesake, the soulknife. It is a psychically created weapon, a shortsword created from the psyche of the soulknife consisting of semisolid psychic energy. If the Soulknife lets go of it it immediately dissipates unless used as a thrown weapon, and the user can create a new weapon with ease to rearm themselves. Skilled Soulknifes can split their weapon up into two blades (though it makes them slightly weaker), imbue them with up to 5d6 extra damage per strike, turn them into bigger swords (long or bastard), throw them, imbue them with enchantments normally found on weapons, attack multiple targets in one blow, damage mental stats on a target and a few other tricks. While these all seem like interesting and fun tricks... when you add them up, the class still sucks. Simply put, the Soulknife is bad. Like, Fighter bad.
The downsides
First, the Soulknife is a full-on combat class, IE it has to get in and keep hitting people with its soulknifes. The first problem with this is that the Soulknife has 3/4th BAB improvement: it gets 15/10/5 at level 20 and you only get that last attack at level 20. This is not good for a class meant to hit things in combat. Next up, while the Soulknife has a d10 hit die it has no heavy armor or any class features that help defending itself, meaning that you're stuck with medium armor and a shield to not die. Its lack of feats (aside from the ones you get normally) mean that even if you try to become better this way you still are very vulnerable in combat.
Next up, the Soulknife is kind of slow using its powers. Until level 5 drawing your Mind Blade is a move action, as is imbuing it with Psychic Strike. So if you want to deal some serious damage at lower levels you've got a bit of a problem. If you manage to live that long you'll become able to make your blades better by turning them into longswords of bastard swords... but this takes a full round action, leaving you doing nothing. At this point you'll also start to notice that the rest of your party starts to swing around +2 weapons when you just got your first +1 bonus last level. And at the end of the day you're still only swinging around a shortsword, whose d6 damage just does not hurt. And at the point where it gets better, pound for pound you still deal less damage than your party's Fighter.
At higher levels Knife to the Soul becomes interesting, given that you can combine it with multiple throwing attacks. This means that you can throw four knifes who each deal 3 damage to one characteristic of your choice, which might net interesting results when you start to damage Wizards and drain their spells, or defeat a monster in one go with a well-placed throw. The obvious downside to throwing its that it's only got a 30 feet range, putting you into trouble when facing long-distance enemies.
Another problem with the Soulknife is that its skills kind of suck: they're all over the place. There are a couple of DEX based skills (hide, move silently, tumble) and the useful Autohypnosis, Concentration and Knowledge (Psionics) that you don't see on other classes... but those are spread out over four different attributes. For the rest you have the standard package of skills, so you can't do something interesting with this.
There is a prestige class for the Soulknife called the Soulbow in Complete Psionics. It allows you to create a bow just like you create your knifes and shoot people with it from a safe(r) distance. This sounds good... until you realize that while in combination with Zen Archery WIS is pretty much the only stat you need for this prestige class but it does zero good for your levels of Soulknife, your bow kind of sucks (a regular composite longbow that cannot be upgraded), the upgrades for your arrows just kind of stop at a certain level, and Phase Arrow (shoot through pretty much anything) is not really worth it.
In short, the only two ways that a Soulknife can kinds work is either as a Fighter but worse (far less attack feats and such) or as a knife-throwing machine that'll fold like wet paper when hit. If you really want to use it consult your DM for homebrewing purposes, but for the rest please stay away from this class. Which is sad, because its concept is very fun.