Free workout tracker Dailymile works fine as a logging and analysis tool for your running, cycling, or other cardio-oriented training, but its highlights are the ways it uses friends and locality to motivate. It's a fairly new webapp, so don't expect to see many friends or fellow runners in your neck of the woods up just yet. But you can use Dailymile to connect your workout notes to Twitter (and, eventually, Facebook and other apps), and keep track of races and other events near you. If disappointing your exercise-focused friend is motivation enough to get you out the door, Dailymile is worth checking out. The site is a little AJAX-heavy, though, and left my Firefox browser chugging to keep up at some points, so don't expect a quick visit from a low-speed or mobile connection.
Dailymile is free to use, requires a sign-up.