ISpinning

ISpinning is a great (and free) little app for road biking and mountain biking workouts. It uses a growing number of body sensors to track stuff like your heart rate (current, average, and max), biking time, calories burned, speed, distance, and power. You can customize the app's dashboard on your iPhone to display just the metrics you care about.

Note: This link takes you to the vendor's site. From there, you can follow the link to the iTunes App Store, where you can download the latest version of the software.

--Mark Sullivan