I personally really enjoy Trackmania too, best free game I've had in years! Loads of jumps and loops (no, not very realistic) and the graphics are pretty good, the lighting and bloom is lovely, especially around sunset.
Trackmania is very good (the version you pay for) - loads of race types and the online play has had a huge amount of thought gone into it. The free one is quite limited on the track types, but give it a go to see if you like the online experience. Zero griefers, but can sometimes lack the excitement of other games.
GranTurismo 5 Prologue is fantastic, but limited by it being a prologue so there aren't many tracks. Plenty of online action but lots of grief players around so can be hard to find a good race. Not as great a leap in AI in single player as I expected either. The F1 simulation though is fantastic and is a real experience with a good wheel.
GTR2 and R-Factor are still around for the PC ultra-sim crowd. Personally as I have a life and don't want to spend 6 hours simulating practice / warm up / qually / 250 mile race and then have it all fall apart because I forgot to hit the pit lane limiter, but lots of people still love it There's a free demo of the BMW M3 around Hockenheim for the PC somewhere based on the GTR2 engine I think - download that and see if you like the style.
I still haven't played GRID or the PGR series, so can't comment on them, though both have legions of fans
I like Grid, it's far better than the earlier Dirt. Although it's not so much fun on lower end GPU's, 8600 or equivalent ATI or below it suffers.
I still play Re-volt on the PC from time to time an excellent old game that still looks pretty good considering it's age.
Aside from it's small number of tracks, I'd say Gran Turismo 5: Prologue. There aren't as many vehicles as there will be in the final version, but it still has over 60 cars I believe. I also love the interface and how it constantly communicates with their network for news, weather, content updates, online events, and videos. They just added a few new cars recently for free such as the Ferrari California, and Lotus Evora. Gran Turismo TV is kind of a cool concept, but I'm not going to pay to watch anything offered on it.
GT5 is fun, but not a real simulator like they claim. Not even close. But it's still fun and good for a console racing "sim".. Online races/time trials change monthly to keep it fresh, and as Heyyou said, they're adding cars every now and then. 72(?) cars now. I tried the GRID demo, but the tracks were rather narrow which would lead me to believe racing online would be a nightmare...blocking, slamming...ug, GT5 is bad enough.
GRiD sux. I played it and the driving physics usually just don't make any sense, I'm not looking for sim quality physics but I do expect to b able to control it normally.
the graphics are fine, but not stunning, they lack detail and good reflections.
"To achieve this exceptionally high level of realism, iRacing.com uses its pioneering, proprietary application of three-dimensional laser scanning technology to create two key features.
Racing.com's sight-pictures are the most accurate and complete ever offered in a racing simulation. You see exactly where you are on the racetrack at any given millisecond, receiving the instantaneous, granular visual input racers require to refine their performance lap after lap.
In addition to its sight-picture visuals, iRacing.com replicates the precise physical features of each track's racing surface. Our laser scanning technology produces a mathematical 'bump map' of the track's camber, cracks, undulations, and patches - recording every millimeter of the surface. A series of "point clouds" capture the three-dimensional profile of the track surface and adjacent curbing.
iRacing.com works closely with major auto manufacturers and racecar constructors to gather exact masses and dimensions for vehicle components, whether outputted directly from CAD data or collected through three-dimensional laser scanning, as well as physical disassembly of the vehicle to weigh and measure parts of the chassis, suspension and driveline.
I agree TDU is also fun and worth the cheap price now.
One thing killing racing games for me is the trend to not include LAN modes. I do more multiplayer racing on a small 4-8 machine LAN than online and lack of LAN in NFS:Carbon and TDU somewhat killed the value for me.
Also, edit: (along the lines of Cuddles comment), it's hard to recommend games without knowing if the preference is arcade, true sim, or a mix. Although I dig both SIMs and arcade racers, my close circle prefer the arcade side of things vs. the frustrating harder to master GTR2, RFactor, or Nascar 2003 type game. Some Flatout 2 on a LAN can be an absolute blast and is fairly easy for almost anyone to handle.
Well, when it comes to the best in racing games then NFS is like a benchmark, for me it is the best racing game that I ever played. However, there are some other games also which I found to be pretty attractive despite their light graphics, these are
3D La Supercars and 4 Wheel Madness 3, which I found at bgames.com.