apple
iControlPad introduces analog sticks to the iPhone
It attaches to your device and pairs up with it via Bluetooth, which means that in theory it ought to work with other smartphones capable of Bluetooth connectivity. Unfortunately, it’s also this Bluetooth connectivity which apparently does not allow official iOS apps/games to work with it, which means you will have to jailbreak your device to enjoy the iControlPad in all its glory.
If you’re interested in getting your hands on the iControlPad, it will cost you $70 and it is available from their website.