I myself use a Logitech G25 mounted on a Playseat Evolution (http://www.playseats.com/)
Just remember that the Logitech wheels do not work with the 360 so if you have one or plan to get one and the next Forza on it as well then id recommend a Fanatec Racing wheel. They are expenisive but atleast you dont have to buy seperate wheels for a 360 and PS3.
Now if you only intend to play racing games on the PS3 and PC then i definitely suggest the Logitech wheels. The best and cheapest wheel is the Logitech Driving Force GT Pro. (http://www.logitech.com/en-au/gaming/wheels/devices/4172)
I would recommend buying from ebay as you will get them cheap brand new from Hong Kong (originals and not fakes). I bought my Logitech G25 when it just came out and paid $250 AU from ebay while they still retail new here in Australia for $300 (rip off). With the G27 that came out not long ago you should be able to get the G25 cheaper. It is one of the best wheels out there on the market so you wont be disappointed with it. Also you wont need to upgrade for a long time (unless you break it).
As for mounting it. There is 2 options. Build/buy a racing cockpit or buy a small table which you can slide your feet under and mount it to the table and off you go. IKEA has tables perfect for them for less then $50. So im sure you can search around and find something. But nothing beats a racing cockpit or a Playseat for a true experience.