I think the ultimate female character from games that I find attractive is Ashley from Mass Effect but since she's fairly normally attractive and her tough attitude is kind of appealing I don't think that needs mention here.
But in Mass Effect 2 there is the OTHER woman I find sexy and let me tell you, that plain messes me up when I think about it, is Jack from Mass Effect 2. If I had been going to pick a girl in ME2 (I didn't, I stuck with Ash) it would have been her and I have no idea why, it's not for her psychotic nature or tattoos or constant swearing or bald headedness. But there is just something about her that I find really oddly attractive, maybe it's because she's tough and angry or because there's a fragile side behind all that... who knows?
But still, compared to this next one Jack is simply eclipsed. In fact all characters from games are suddenly just angry high schoolers in this competition now, for the one above all others of whom my attraction towards deeply horrifies me and this is Lisbeth Salander from The Girl with the Dragon Tattoo. This girl is messed up, angry, socially distant and very very violent. She has horrible things happen to her every day and she enacts violent vigilante justice on people which can include violently tattooing insulting words into them and once or twice allowing them to be set on fire (she does this only to real scumbags though). She's also very smart and can show an occasional bit of compassion but overall she is dangerous with a capital D.
Plus, in the original book (I only saw the film) she was much shorter and despite being about twenty six she looked about fourteen so there she is, the number one woman I feel really horrified about my attraction for.
What does it say about me that most of the women I find attractive would probably murder me if I tried to make any kind of move on them?