The WiiChuck Adapter is a small PCB that is designed to be inserted into the connector of a Nintendo Wii Nunchuck to provide access to all 4 wires of the remote. The power, ground and  two-wire interface of the Nunchuck are all broken out to a 4-pin 0.1"  pitch header.

The Wii Nunchuck is loaded with features -- a 2-axis joystick, two  buttons and a 3 axis ±2g  accelerometer -- and any device capable of I2C  can communicate with it! The WiiChuck allows you to interface with the  Nunchuck without making a mess and cutting the wires.

Note: This product is a collaboration with Tod E.  Kurt. A portion of each sales goes back to them for product support and  continued development.

Documents:

• WiiChuck Homepage (great tutorials and Arduino library)