I don't have an XBox of any kind and only a PS2 and Wii, but I'm very intrigued by the Portal games. Are they worthwhile on the PC, or is it one of those games where the controls really don't work well except on a console?
Portal 1 is probably slightly better on the PC due to a few puzzles that needed some quick reflexes, but I'm pretty sure that both have the option to use a gamepad if you prefer. Likely both compatible with the 360 controller, too.