Mapmyride.com is a pretty cool website for cyclists. It allows you to (you guessed it) map your routes and get exact mileage, calories burned, average pace (if you enter duration), and log your workouts. You can search routes that others have entered, and publicly share your favorite routes. It keeps a log of the rides you enter and tells you your total cumulative distance traveled, how much gas you saved by biking that distance, what the cost of that gas would have been, and the carbon offset.
Pretty cool stuff! I've been using Google Maps to map my routes until now, and they only let you choose between driving, public transportation, and walking. I'm happy to have found a biking-oriented site!