The Wii Nunchuk is designed to work together with the Wii Remote on the Wii console. Contoured to fit perfectly in your hand, the Nunchuk adds extra buttons, an analog joystick, and additional motion-sensing control to expand the game play possibilities. It is also an "I2C" type device which makes interfacing to the Lego Mindstorms NXT easy. You can pick-up a Wii Nunchuk from eBay for under $10, and a pack of 5x NXT Compatible Male Plug from Mindsensors for $5.95. In essence a new NXT Sensor/Controller for under $20.00.
I produced the original NXT-Nunchuk Hack a couple of years ago and have posted details on the old NXTasy forum, but due to NXTasy's demise and the fact I never till now posted the instructions on my blog. As I've had a couple of quires
Actually, now you can get a mock nunchuck for $4. For a three axis accelerometer (+-3g I think), analog joystick, and two buttons, I would say that is a bargain, not to mention it already has an I2C interface. Apparently all you have to do is replace the pullups to make it work with the NXT.
For more details, including the NXC and RobotC Drivers, and my other Mindstorms Robots, please visit my Blog: www.rjmcnamara.com
All that is needed now is for someone to build a NXT-G Block to suite the NXT-Nunchuk..........