AllSport GPS, by Trimble Outdoors
Price: About $6 per month, prices vary by device
This app lets you hit a start button on your GPS-enabled iPhone, Android or BlackBerry device, then you do your workout (walk, run, hike). When you're done, you can view results such as time, calories burned, maps and number of miles traveled. Results can be stored online, letting you compare with past workouts. Other workouts can be downloaded to the phone from experts and other users. Having the app on the phone eliminates the need to carry a pedometer or special watch.