Forza 2 - Best racing game I've ever played and is so much better than Gran Turismo, very underrated IMO.
Halo 1 - Spent too many hours playing this game, I never get bored of it even to this day, some of my friends say it's one of the worst FPS games they've ever played but to me it's one of the best!
Call of Duty Modern Warfare - The first Modern Warfare, this game is my favourite FPS of all time, a lot of my friends say Black Ops is better and even Modern Warfare 2, they don't compare to it TBH