Comment Ridewithgps.com (Score 1) 188
I do a decent amount of cycling and have a Garmin 305 that tracks heart rate, cadence (pedaling speed), location, and time. I always thought it would be a lot of fun to play with the data, and have been working on a site for a while with a couple friends that has some cool features (mouse over your elevation and see where it is on the map, determine time spent in heart rate zones, estimate power output in watts, calories, put it on a calendar - currently working on finding other times you rode the same section of road and race yourself)
Without a GPS unit, you can draw a route and we pull elevation data off our server if we have it (we have the continental US in 1/3 arc second accuracy, pretty good), estimate instantaneous grade, etc... fun project and people are finding it useful
Anyway, check it out if you want: ridewithgps.com