Found this in this morning's Baltimore Spokes netletter:

Greater Greater Washington - Ride the District

Ride the City has officially launched in the Washington area. Their tool plots bicycle routes, combining map directions and knowledge of bike lanes and trails to recommend safe routes.
Some of the comments at the GGW link make it sound as if there are bugs to be worked out, but it seems that there's a lot of potential if they get the sort of feedback they need.