There's a ton of them out there. Scroll back in this news group and you will see quite a few links, this question gets asked frequently. Or if you're really lazy, just try this one, it's as good a place to start as any: http://www.scgtworld.racesim.net/
Ya know, as many times as I've seen this question asked (and answered) I've not seen this site mentioned. I wasn't familiar with it. But it looks like a good one.
rec.autos.simulators is a usenet newsgroup formed in December, 1993. As this group was always unmoderated there may be some spam or off topic articles included. Some links do point back to racesimcentral.net as we could not validate the original address. Please report any pages that you believe warrant deletion from this archive (include the link in your email). RaceSimCentral.net is in no way responsible and does not endorse any of the content herein.