For a racing game I am waiting until January for Burnout: Paradise. IF you want a simulation (read: boring) game, then I am not sure. As for a Rally game, I am betting that you should wait until early Oct for Sega Rally.
November has Ace Combat coming out - what should be a sweet Top-Gun style airplane game
Gears of War - must have 3rd person shooter
BioShock/ Halo 3 - must have 1st person shooters
Check out sites like
www.ign.com or
www.gamespot.com or
www.gamerankings.com for reviews before you buy games. Generally their reviews are spot on.