Mine would have to be Morrigan from Dragon Age: Origins.
Firstly, she is voiced by Claudia Black - who's voice is hot enough to melt a cheese sandwich from across the room.
Secondly, her personality isn't all sugar, spice and all things nice. Don't get me wrong, she has a nice side - but it's all hidden behind Darwinist ideaologies.
Thirdly, there's her looks. The clothing. That cool looking skirt, the feathers upon her shoulder and those beautiful golden eyes. (Afghan Girl eat your heart out...)
On paper, she's just a mean spirited cow - but in reality, she's nothing short of glorious. (I know a girl who has a similar personality and dress sense and boy howdy, I crush on her.

)