During PAX East, PowerA actually gave away free blutooth Android MOGA Controllers. This "pocket" edition has dual sticks, two shoulder triggers, four buttons, and a start/select button.
It requires that you download a free "MOGA Pivot" app that has the drivers and its own little mini-marketplace for MOGA-compatible games, however the MOGA can also be used with emulators such as Super GNES (I had to tinker with the settings a bit but I was totally playing Chrono Trigger with my MOGA at some point).
I think it's really cool, but the only drawback would be that some batteries like the one on my old Droid Bionic don't have enough capacity to support extended amounts of play time.
They're actually going to have a Pro edition that'll sell for $50, but that's later this month, if I remember correctly. I've had a lot of fun with it so far but I'm not sure if I'll go all the way and get the Pro edition. Anyone else here try it?