Update: If you're reading this, you might also be interested in the new Wii Fit.
Anyone who's played Wii Sports on the Nintendo Wii will no doubt notice that a game of tennis or baseball or boxing does take a fair bit out of you. This guy even did an experiment to see if he'd lose weight by playing it regularly. Who says video games are bad for you? If this appeals and you haven't got one already, get a Wii here.