I recently bought a nexus 7 and was able to load every game across all my systems that I own (excluding Xbox 360) onto it. However, the touchscreen controls are horrible, and as of android 4.2.2, Wii controllers are broken (plus, I don't terribly like the feel of it, and there's not enough buttons). The only controllers I really like for emulators are 360 controllers, but I can't use the USB port because that's either used for charging or storing Roms. Thus the idea of a Bluetooth 360 controller. Seeing all the things you've done with Xbox controllers in the past, I figured this should be somewhat easy.
Attributes:
Xbox 360 controller, preferably black
Bluetooth instead of the proprietary radio that microsoft uses
Compatibility with Android/Nexus 7