Burnout 2: Point of Impact. This is one kick-ass racing game. I don't think it's online, though (you can only post scores). Burnout 3's due out sometime in the next year, and it's sure to be kick-ass. Otogi: Myth of Demons was a great game, as well. And, if you don't have a PlayStation/PS2 already, DDR was released for XBox.

BTW, are you getting XBox Live?