Where to purchase the best Controllers?

[lahawtho]

I was wondering where I could purchase a controller to run Nestopia or Rocknes? I need one that is USB. I also wanted to know how to change the keyboard configuration if I don't get a controller. I don't see how to do it with either nestopia or Rocknes. Also how do I know if the controller will work. I've seen how an snes controller works with SNES9X but can't see how I would configure a controller if I got one for Nestopia or Rockness. I'm running a mac G5 if that helps any. Hope I included all important information needed.

-luke-