Pedometer!

Run, walk, or jog your way to better health The Pedometer application will help you lose weight and stay healthy as it tracks your steps, distance traveled, and calories burned all conveniently from your iPhone or iPod touch. A built-in stopwatch mode allows you to time your training sessions while it counts laps, distance, calories, and speed. Now with GPS support for even better distance tracking Continued use of GPS running in the background can dramatically decrease battery life.