Why remain stationary when you workout when it's possible to convert that energy into covering some space? This is the main idea behind bodybuddy's Streetstepper.
It's a cross between a bike and the stepper machine you see at the gym. Your stepping motion is what makes the bike work.
If you've suffered from back and neck pain from a regular bike, you might like the Streetstepper better. You're not hunched over like on a bike, but rather you're in an upright position, just like when you're walking. It looks so graceful. Check it out.