I just bought Infamous 2, loved the first game, the second is crazy and super fun. i know it's kinda old, but i never got around to playing. Love the relatively free roaming-ness of the game. i prefer it to linear walkthroughs.
I'd have to say DiRT 3. The more I play, the better I get at steering, cornering and anticipation.
Having 5.1 is a big help - can determine where someone's trying to overtake me from