In the beginning, there was Sports Car GT, and it was good. Then came EA's F1 series. It was not quite so good, but was still pretty fine.
Image Space Inc., or ISI to their friends, have been working on race sims for a very long time now. Sports Car GT is a classic of the genre. Having broken ties with EA, ISI are on their own, and producing rFactor. With the First Racing debacle of suing modders and their various other SS style business tactics (including changing their name), a lot of folk are turning to rFactor as the one true hope for PC race sims. An opinion not misplaced it has to be said, after all, ISI have always supported modding, unlike Kaemmer's gestapo regime, and modding is the lifeblood of the PC race sim community. Games with mods live. Games without die.
Here's an unofficial feature list for ISI's upcoming opus. (Ironically posted on a forum that, to many people, appears to be run by Kaemmer's unofficial fan club these days.) The title is still in beta right now, so obviously these features will change over time.