The most competitive out there by far is iRacing.

IIt isn't as expensive as it looks, as it has discounts all the time, for everything and for doing nothing.

Trackmania no?

one of my friends from teamdignitas plays tm, i suppose it depends on what kind of 'racing game' he's talking about. I mean it is racing, but not exactly realistic :D http://twitch.tv/dbergie

Trackmania and iRacing according to this thread

Have a look on this car forum lot of them playing i-racing with pretty pro looking rigs. Ironic given most of them own Skylines in real life :)

http://www.gtr.co.uk/forum/222266-anyone-have-pc-racing-rig.html

If you like stock car racing and don't want to pay every month like iracing (looking at you too quake live) then NASCAR racing 2003 season is probably the most active NASCAR sim out there. It is probably the most realistic oval racing sim after iracing, and it has a huge mod community with cars and tracks and even different types of racing such as gt racing.

Definitely take a look at it if you don't mind playing an 8 year old game that is as good as any new sims.

thanks i will take a look for the moment I'm playing DiRT 3