It feels a little like Big Brother, but in a good way. The RunKeeper app tracks your outdoor runs using your GPS-enabled iPhone. It calculates calories burned, distance traveled, duration, pace and altitude and even traces your path on a map. All your workouts are stored over time, so you can monitor your progress and identify areas for improvement. The app also has built-in iPod controls, so you don't have to exit the app to shuffle through your playlist. If you're not the outdoors type and prefer slogging away on a treadmill, RunKeeper will still track your fitness stats.