Don't smirk at the price – we found this to be the absolute best way to run indoors. Gliding naturally on a 17-inch belt (that lasts 150,000 miles) without electricity, you control your pace by positioning your body. It takes a moment to get used to the floating-on-air sensation, but running on a Curve can burn 30 percent more calories and engages more muscles than a normal treadmill. [$5,950;]