The Prince (PoP: The Sands of Time )-A genually believable character, who is funny, not for spoiting one liners, but for being a posh moron. All this, and he's so likable.
GLaDoS (Portal)-Some of the funniest lines I've ever heard in a game, a character who goes from slightly creepy to dam psycotic. A robot with more personality than half the video game humas out there.
G-Man (Half-Life 2)-He's so fucking weird and creepy. I hope the mystery of G-Man is never revealed, it would ruin the character.
Adam Ryan (Bioshock)-A villain you agree with, and eventually come to respect. Such great ideals, all gone so, so wrong.
Raz (Psyconauts)-I loved that kid, simply for being so determinded and badass.
The Companion Cube (Portal)-*Lowers his head in respect* He touched my heart, and he never said a word.
EDIT: Oh! Wait
Reever (Fable 2)-Alright, he hasn't got much competition, but he's best character in the game, and one of my faviourite characters in a game. Can Stephen Fry do no wrong?