If you like to play games on your Mac, you may tire of using the keyboard and mouse and not like the available third-party controllers available for OS X. Instructables user fungus amungus shows how you can adapt either a wireless or wired Xbox 360 controller to work with your Mac.
The basic process is the same for wired or wireless controller use with the exception that you'll need a wireless gaming receiver if you want to be wireless. You'll use a USB driver utility called Tattieboogle to recognise either the controller or receiver and a $5.49 app Joystick Mapper to get the controllers working. After that you should be good to go, though with games you may have to spend a few minutes remapping the buttons before playing.
Use an Xbox 360 Controller on OS X (wired + wireless) [Instructables]