Project Wildfire is a now defunct website that offered many great downloads in mods they created as well as some great tracks and much more.  While their site is down their files still are very much alive and available.  Here are all the tracks they created that I have collected.

Bowman Gray Stadium
Evergreen Speedway
Chicago (IROC series)
Daytona (IROC Series)
Hickory Speedway
Homestead
I70 Speedway (v1.0)
Indianapolis Raceway Park
Indianapolis (IROC Series)
Mansfield Motorsports Park
Martinsville Speedway 2004
Mesa Marin Raceway
The Milwaukee Mile
Nashville Speedway
Talladega (IROC Series)
Thompson International Speedway 2003 v1.0