"Are you still into video games? You seem to look... different"

Here's one in the category "Why didn't I think of this before?" The FP (as in 'First Person') GameRunner not only helps you work out while playing first-person shooter games, it forces you to.

The treadmill functions as a controller, replacing the 'walk' command with the treadmill function itself. So if you don't want to die, you'll have to keep running. Literally. Steering and shooting controls on the handlebars help you survive in cyberspace.

Meanwhile, in the real world, you start to look increasingly like your avatar, with legs like tree trunks and a sixpack for a stomach. Plugs into your PC's USB port and works with any first person shooter.

But wait, there's more! It also folds under your bed. Seriously.