Have a few, really:
HK-47: Knights of the Old Republic 2-humor factory, and his annoyance at his old companions from the first game
Kreia: Fantastic voice actress, and genuinely well-written, with an understandable motivation, and one's that's better than arrggh! Dark Side!
Boone: Fallout New Vegas-once you get into his (depressing) back-story, you feel sorry for him, plus he's the only companion that isn't trying too hard to be funny.
Da'kkon-Planescape Torment-fantastic back-story with the Circle of Zerthimon, and his enslavement. Also badass "bro" moment once you get him through the final level of the Circle.
Vhailor-Planescape Torment-combat monster, and the very definition of lawful neutral. Looks pretty spiff to. I kind of linked his single-minded pursit of justice... and how you can destroy him by convincing him it's meaningless.