Peripheral company Zeetoo is coming up with a Nunchuk-like device for cell phones. The Zeemote, that's really what it's called, no lie, will connect to select cell phones using Bluetooth. The controller has an analog stick and buttons in a Nunchuk-shaped device. The company says they also have a motion-sensing version of the controller in the works and another prototype that will have a tracker ball.
Personally, I don't think it's the lack of controls that is keeping mobile gaming from realize the potential that mobile game developers are always harping endlessly about. I think the real problem is the lack of a single operating system, something that, dare I say it, the N-Gage platform might actually help fix.