This is the source material if you are unfamiliar with P&P:
http://en.wikipedia.org/wiki/Complete_Arcane#Warlockhttp://en.wikipedia.org/wiki/Warlock_(Dungeons_%26_Dragons)#Dungeons_.26_Dragons...HP=D6
Saves=Good Will, crappy Fort and Reflex
Alignment=Any Chaotic
Skill points: 2+int/level
Proficiencies: Simple Weapons and Light Armor
BAB: 3/4
Casting Stat: Charisma (kind of. Cha determines DCs, but is not actually required to cast, so it is painlessly dumped if you stick to invocations that don't allow saves.)
Features:
Eldritch Blast - Spell-Like-Ability (Should be enhanced by appropriate metas by DDO precedent. (Not P&P precedent)) Ranged single target blast deals d6/2 levels untyped damage. Can be enhanced by 1 blast shape invocation and 1 blast essence invocation (see below).
Damage reduction - #/cold iron, scales with level.
Energy Resistance - (Like Fvs)
Fiendish Resilience - Fast healing.
Deceive Item - Awesomeness at UMD. Artificer level or better.
Invocations: spell like abilities that can be used at will. Some modify your eldritch blast and the rest simulate arcane spells but have an extra effect and/or evil flavor. They come in 4 different strengths ("levels") and you only get 12 of them by warlock level 20 (hopefully DDO will up this to at least 1 per level.) I will post specific ones from P&P if I can find a text to cleanly copy paste, but you can expect to have invocations that resemble blur, ddoor, dispel, charm, animate dead, true seeing, wall of fire, shadow walk, invisibilty and others.
Also the essence invocations add a energy type and special effect to eldritch blast: the acid one bypasses spell resistance, the cold one gives a dex debuff if they fail a fort save. (There are many others.)
Then there are the blast shapes, which include channeling through melee, cone, ray, chain, line, and emanation (think energy burst.)