Tali from Mass Effect was pretty cool, getting into her discussions were geniunely interesting and since she wasn't a "dating prospect" her character managed to progress a bit better and had to be a bit smarter.
Alyx Vance - Well-written, strong and sympathetic? or just a crass, cynical creation of an "ideal female" designed by listening to comic book nerds chat about their preferences?
Hard to say. I think Alyx might be a bit too ambitious actually. She's strong, cool and very human. Awesome, but she's also female and that's very much at the forefront of who she is. Her gender was a huge part of defining her personality. I'm not aware of modern feminist leanings, but is it realistic and awesome that a woman is embracing her femininity and still playing with the boys? Or is her gender an inescapable handicap in a man's world that unfairly colours every awesome thing she does as "cool, for a girl"?