Forget Wii Sports and the Balance Board. If you really want to sweat your weight off you only need a NES, a Mike Tyson’s Punch-Out! cartridge and a properly wired boxing dummy:
I wanted something I could actually play as if I was punching the person I was playing. This led me to modifying my Slam Man Boxing Dummy to add arcade buttons I could punch.
The hack itself is quite simple, but ingenious and definitively effective for both the gameplay and doing some actual exercise.
[Instructables via Make]