I like this America's Running Routes app from the USA Track and Field web site. It's a Google Maps mash-up that allows runners to map their favorite routes, save it to the database, and share with other runners.
The mapping app has an easy-to-use, point-and-click interface, and shows mile markers along the route. Runners can input attributes (flat, hilly, etc.), rate the routes, and read other user's reviews. Check it out: