Well, they're all racing games but I can't stick to cars alone so:
1) Microprose GP500 (older but still the most realistic bike sim)
2) TOCA Race Driver (very nice touring car sim, not the most realistic but definitly fun)
3) Need for Speed series (the first two were the best IMHO, altough I also enjoyed NFS Underground I must admit)
No Project Gotham, Midnight Club or Gran Turismo cause I just have a PC and no game console...