Wii RetroPad Adapter is a Wiimote adapter based on a small PCB, an ATMega uC
and a couple of connectors that allow you to use the following classic
joysticks as if they were a Wii Classic Controller:
:. Sega Genesis pad(also supports: Sega Master System, Atari 2600 and others)
:. Nintendo NES pad
:. Super NES pad or Playstation 2 Dualshock, depending on the extension cable
used and uC firmware.
The Wii RetroPad adapter talks to the Wiimote that, ultimately, talks to the
Wii wirelessly, so you get a real Classic Controller experience with no Game
Cube extension cables involved! 
This adapter is compatible with both Nintendo official games ans also homebrews
(AKA, those great emulators out there!).
If you are going to use a PS2 joystick with it, it even supports the analog
sticks!
Wii RetroPad Adapter is Opensource / Openhardware, so you can contruct your
PCB, compile the source code, burn the firmware in the micro-controller and
start using it.
https://gitorious.org/wii-retropad-adapter
Enjoy! 
bootsector