Best RACING games for XBOX?

[BenSkywalker]

(But, if you didn't like the first one, or Rally racing games in general, then there's nothing here to change your mind.)

CMR '03, CMR '04, and RS are all in my library and I certainly had the most fun with RS- although I liked the tweak element of CMR '04 better then RS(being able to set up my car to my liking is a big plus).

 

[RedRooster]

TOCA 2 was pretty good, it had more sim-ish physics than PGR2 with a lot of different car/truck types you could race. PGR2 was also a really good quality fun arcade game with tons of cars to unlock, while being relatively difficult to get all platinum medals(I did eventually). Colin McRae 4 was good too, I still have it, but it's still not near the hardcore sim I'm looking for. Richard Burns Rally is supposed to be just that, but it's only out in the UK right now(although I suppose if you have a modded Box...).
MX Unleashed is a fantastic MotoX game, from the makers of Motocross Madness(the old MS series).

MotoGP2 is currently the King of all XBox racing titles though, it's perfect online integration can't be debated. Granted, you have to have interest in motorcycles to like it(I'm a MotoGP diehard).