Hey from Fatwallet
iracing.com always sounds very cool, although I've never tried it because of the whole pay-to-play thing.
Other than that, as mentioned, the GT* games in general are good. GTR: Evolution is somewhat newer, really just an expansion to Race07, but it has a semi-active modding community - you'll find things like a conversion of the M3 from BMW's M3 Challenge, conversions of all cars from GTR2 and GTR: Legends, and even the Top Gear test track. For me (I have a G25), this is where I've spend most of my 'sim' time. Same as with all the games in this series, nothing else recreates the feel of actually being there quite as well.
There are other games that aren't strictly sims that are still fun - Need for Speed: Shift being one of them. I'd recommend Test Drive: Unlimited over that, though... The ability to drive a high-end car (both of these games have good selections) wherever you want - highways, back roads, mountain passes, city streets - even if it's not the most realistic game, it's still a lot of fun.