I came across this cool little program recently which calculates heaps of data on your workouts. It uses your phone (gps enabled, iphone version coming soon) and tells you your route, distance, speed, time, altitute, max speed, min speed, etc, etc and you upload it to the web (or keep it on your phone) so you can analyse your workouts and keep the data.

www.sportypal.com

You can also look at other peoples data if they share it as well! It makes me want to go faster and get a better time each time I go.