Map My Run is a great site that allows you to map and plan your run!  You can also calculate mileage, count calories and find runs locally or around the world.  Not only can you map runs, but also bike rides, kayak and canoe routes, skate and swim routes.  You can also use it after you run a course- just remember your route, punch in some points, and you have a highlighted map of where you ran and how long you ran for!  It's a fun site- and beats driving around in your car to figure out how long a route is!