Burnout Paradise is a good'n that I play with my sister every once and a while, it's "party mode" is a lot of fun... Street Fighter 4 recently was released for PC, which is awesome
and the Guilty Gear Series is another good fighter... I currently have Guilty Gear X2 #Reloaded installed right now, and am certain that it has 2 player capabilities on the same compie. I guess I haven't played more than 10 minutes of it, but GRID looked like a good racer, and I wouldn't be surprised if you could do split screen or trade off in that game, don't take my word for it, though... Enjoy, I suppose!