Map My Run
You don't have to be a runner to like this mapping/distance site recommended by the folks at Fit City Madison. Map My Run uses Google Maps to figure the distances for routes you intend to traverse, whether by foot, bike or pogo stick. And if you like a cross-country ramble, it's useful for figuring all manner of off-roading, just by dragging the mouse wherever you plan to go. Sure, you could use a pedometer, but the low-end models depend on accurately figuring your stride (iffy); plus, you have to walk the walk - you have to go the distance before you know the distance. Map it here first and know before you go.
The interface is a bit clumsy, but with some experimenting, most functions become clear. Also check to see what routes other users have liked and saved on the site; it's searchable by ZIP code and route type (walking, running, biking, dog walk, horse trail, etc.) Useful for travelers who want to have an outdoor workout at their destination, or newcomers anywhere.