Admit it. You've got an old GameCube from yesteryear laying around, and the slow economy (and fear for your life) is holding you back from running to your nearest brick-and-mortar to pick up a Classic Controller for your Wii. You know you want to play Super Mario 64 to work off that turkey, but you can't justify laying out the cash. Fret not; YouTube user marcan42 has you covered, courtesy of a PIC18F4520 microcontroller and makeshift GameCube connector, along with a chopped off Nunchuk extension cord. Of course, you could just pick up a different model, but that would be way too easy. We didn't say it was pretty, but if you're still intrigued, check the full vid after the break.
Update: As a bunch of commenters have pointed out, this can be done already by plugging the GameCube controller directly into the Wii. However, this mod lets you do it wirelessly -- err, if you don't count the big microcontroller and mess of wires.