I think most people reccomend the Xbox 360 controller for the PC. Wired or wireless, your choce.
www.amazon.com
Stupid question: is there an adapter for the wireless controllers to connect to a PC? Are they bluetooth or something?
Yes, but they've been hard to come by. They come included in the Wireless 360 controller for windows package, but they're not sold separately anymore. Your best bet is to check out ebay.
It's also been reported quite a bit that the wireless is rather buggy on the PC. Best to stick with the wired version.