HiPhish: In essence any USB device that conforms to the HID standard should work. I have a Logitech F310 gamepad and a Logitech 3D Extreme Pro joystick plugged into my Mac, both worked out of the box even though they don't officially support OS X. They came with driver CDs for some special software and drivers, but I didn't need any of that. I guess if you want to do button mappings outside the game that could come in handy, but I never needed that, so I have no no idea what the software on the CDs even does.

Of course if the game has crappy programming it will be a matter of luck whether your controller works, but that's the fault of the software, not the device.

And if you want to use the XBox 360 controller, that won't work out of the box. There are unofficial drivers, so if you have a controller to borrow or if you can return it back to the store you could try the drivers out:
http://tattiebogle.net/index.php/ProjectRoot/Xbox360Controller/OsxDriver
https://github.com/d235j/360Controller

Some gamepads can work in DirectInput mode and XInput mode. My F310 has a switch that lets me choose. The XInput mode is the one that works like the XBox controller, so that one isn't working out of the box. DirectInput works fine, but the analog shoulder buttons only register as digital. That could be an issue if you intend on using the analog buttons. Maybe it works with the unofficial drivers, never tried it out.