My favorite ability drainer build that's likely to be allowed from low levels (if your GM allows Evulz characters) is thus:
Build
NE or CE Warforged Cloistered Cleric1/WhirlPounce Barbarian1/Psion (Shaper)1/Warblade3/Soul Eater1/Bloodstorm Blade4/X9.
1: {Murky-Eyed}, {Shaky}, -=TRAIT=-, -=TRAIT=-
1: [Devotion: Knowledge, Domains: Elf, Travel], [Turn Undead]
2: [Pounce], [Whirling Frenzy 1/day]
3: [Psicrystal Affinity: Nimble Psicrystal]
4: [Weapon Aptitude]
5: [Uncanny Dodge]
6: [Battle Ardor]
7: [Energy Drain 1]
8: [Returning Attacks], [Throw Anything], [Weapon Aptitude]
9: [Martial Throw], [Thundrous Throw]
10: [Fighter Bonus Feat]
11: [Lightning Ricochet]
Roles
You start your career as an archer (or a front liner, if you feel frisky). You eventually learn to harness your inner rage and make things go splat. You feel a momentary touch of enlightenment as you learn to create Black Lotus Extract by the gallon (via psionic minor creation) and cover yourself and your items in it. Then you focus on being a melee dude for awhile (complete with poison!), and can even nab Iron Heart Surge or White Raven Tactics (via trade-ins) before headin' off to bestow negative levels upon people, and even being able to throw those melee weapons and treat 'em as melee attacks.
More Warblade helps for maneuvers. Dipping Crusader1 or 2 gets you Thicket of Blades (depending on DM interpretation). Paladin of Slaughter2 would go well if you had the CHA synergy, and you probably don't. Taking Soul Eater to 7 means you bestow 1 more negative level per hit, but death ward is probably very common by that point.
Your feats help determine your role. Soul Eater requries Weapon Focus (body part), and you conveniently have a slam attack. Practiced Manifester helps make your poison last longer. Precise Shot aids with ranged combat. Etc.
Build 2
LE, NE, or CE Warforged Psion (Shaper)6/Ghostbreaker3 (Hyperconscious 136)/Soul Eater1/Ghostbreaker+2/Shaper+X.
Roles
You're a Psion, pure and simple. You have metamorphosis from power research or Expanded Knowledge. You have Psicrystal Affinity because having a crystalline minion with a radar-like sense, the ability to take Mindsight and Lifesense, and who provides you with the Alertness feat (for Soul Eater) is just plain wonderful. Soul Eater is there so you can turn into a creature with many attacks (hello, Pyrohydra/Cryohydra!) and inflict negative levels. Add Metamorphic Transfer, Practiced Manifester, and other abilities to taste.
If you're CE, take Anarchic Initiate levels instead of Shaper+X! You get more HP, more skills, and notable class features. Remember, Psychic Enervation only applies to Wild Surge, not Overchannel or Chaotic Surge! You, of course, will need Overchannel, but that's pretty spiffy and you'd probably get it anyway.