Cost: Free (basic version)
Walkmeter Walking & Hiking GPS tracks your steps and cadence using just your iPhone. You can even view traffic maps using Google Maps (your phone must be connected to 3G or GPS) and get a calorie count after your activity. It's not just walking or hiking; you can also track cycling, running, skiing, and other activities. While the basic version is free, you can access advanced data features with the Elite upgrade.