Get the Codemaster Racing Pack.
Quite worth it for 5 racing games.
DiRT 1 and 2, plus GRiD makes the pack worth the money.
IMO, the racing games i think that is worth buying are:
GRiD: Very good game play with multiple classes like GT1 to drifting to 24 hours(actually in minutes) Le Mans.
DiRT1: Much more old school, like older Colin Mcrae Rally games like damage on car carry to next stage and much more extensive tuning. Plus some really fun trucks to use like the lorry race, which was not featured in DiRT 2
DiRT2: Better graphics, and trailblazer. Rally was dumbed down a bit, but still fun. Trophy Trucks are actually drivable now, but it was hell to drive in DiRT 1.
NFS Shift: The handling physics is similar to driving in real life like the camera actually tilts a bit when you drive over a bump. It is more for immersion, IMO,and pretty accurate car handling. I enjoyed this one a lot too.
Trackmania United Forever: This game is not free, but i think it worth the price for buying it for 7 different environments that feature different types of cars. Best racing game for Multiplayer, as it uses Dedicated Server system, not P2P like other racing games. Also, you play this game smoothly even with ping over 2000. Trackmania as no local servers, but it doesnt matter as you can connect all the way to German with no problem. It still have a very active community like 30,000 on peak to about 8000 on lowest peak. It's also a great game to play competitively,not just casually. The only downside is, there is no collision in this game but its more like for the sake of fair competition.
Trackmania Nations Forever: This is the free portion of Trackmania that only give you one environment. Other than that, it's the same.
tl:dr: If you want to play MP, Trackmania is no doubt the best choice. If you want SP, DiRT1 and 2, GRiD are the best games to play.
I prefer those who are more sim-like racing games. Arcade games are ok too, but there isnt much choice other than Flatout 2, NFSU and NFSMW. Havent tried Split Second or Blur.
WOW!!! Thanks for the long advice...
But I got Dirt2 already... erm... if I dun have Dirt2,I might inclined to get it... decision decision... will wait until last day to decide...I got
Momo Racing wheel.. intend to buy more racing sim...