World Track Database

hugos

a bit old but has a few gems ... for the general culture of people who like the tracks!

(also contains Hillclimbs)

http://www.silhouet.com/motorsport/tracks/tracks.html

andylaurence

http://www.gdecarli.it has a bigger database and track maps of a large number of them. It's actively updated and there's a forum to post new info you may have.