This crazy small bluetooth wireless game controller for Android and iOS devices is small enough to fit comfortably on your keychain and also doubles as a key finder. Black Powder Media are the brains behind the pint size Android Controller and put their project out on KickStarter earlier in 2013 when it managed to raise significantly more than their target in no time at all.
The iMpulse Controller features a D-pad, 4 action buttons and a pair of triggers that sit on the back. No start or select buttons in sight unfortunately (curiously missing from most Android Controllers). The iMpulse controller also has a cover that can act as a stand for your device, reasonably well.
As far as game support is concerned, there are a couple of points to note. First, all emulators play really well with the iMpulse Controller. However, the first revision of the firmware worked only with emulators. It did not support HID, which is supported in a number of games as the native Android Controller bluetooth protocol. It is worth nothing, however, that the firmware was recently updated to support HID. The instructions for updating the firmware are available at the iMpulse Controller website, here. This requires a Windows computer that supports Bluetooth and isn't necessarily a trivial task.
Despite the lack of HID support out of the box, the small size and portability of the controller combined with what appears to be some really good thought put into the hardware design of the thing, the iMpulse Controller could be a mighty Android Controller in a tiny form factor ready at your willing for some good ol' Mario Kart or Street Fighter action.