Get a Logitech F310. It's pretty cheap, good enough quality (not spectacular), and has a switch for two different modes of operation. In the first one, it's a standard USB gamepad and works with most games as-is, just plug and play, and no dorking around with beta/buggy/broken third-party drivers. The other mode is the equivalent of an Xbox360 pad, which does require dorking around with those drivers, but you do occasionally find Mac games that were inappropriately programmed to only work with Xbox360 controllers, so it works with those too. It is wired though, so if you really need wireless it wouldn't be for you.
--Eric