Logitech G27 steering wheel http://www.cybernatic.co.za/product_info.php?cPath=98&products_id=724
Look at which games supports a logitech g27 not all the games supports the entire clutch system and all.
I don't know of any good simulators on pc
Gran turismo and forza 4 is very good but thats ps3 and xbox exclusive.
I play racing sims and rFactor is my favourite - go download cars and tracks from rfactorcentral.com. Be sure to d/l Kyalami track, its a bit outdated but it's very good! CTDP and Endurance series are top notch. This sim is so good, Formula1 teams use it (the pro version). I also find Live For Speed to have great physics. The simbin series are also really great: GTR2, Race WTCC, etc. I am currently waiting for rFactor2 to get released officially.
BTW there is an active sim racing community locally called SARL who race rFactor on local servers. I used to race there when I had time - they are very professional and skilled! They are based on the saix gaming forum, see http://games.saix.net/forum/viewforum.php?f=29
The G27 is a great wheel, but expensive. The Driving Force GT doesn't have the clutch pedal or full gear**** (only up/down and buttons on the wheel) but it costs about 1/3rd of the price so it depends on your budget. As for the games recommendations, it seems only TobyK read the OP since the others are recommending arcade-style and/or console games. The most realistic simulation game out there is probably GTR2, although it's a little old and I don't know how many people play that online. The F1 games are also pretty good and I think there's even a group of people from MyBB playing (or there used to be). Need for Speed: Shift 2 is also pretty good. Not as realistic or detailed as the others (similar level to Gran Turismo 5 actually), but it's pretty fun in its own way.