Are you trying to *choose* a route or to *display* it?
As far as I know, there is no one good place to choose a route. Google maps added a very limited bike route feature, but it really just gives roads/trails that are allowed, not ones that are good. To figure out which the good routes are, you have to do specific research about the specific location. Most US States Departments of Transportation have some info on designated bike routes in the state. There are guide books and maps for cycling (Adventure Cycling, LOnely Planet, Pedaler's Paradise, Bicycling the Pacific COast are some examples) for specific locations. But i've never seen a site where you can just pick points and it gives you a good bike route. There's just too much involved with picking good roads, and it can be a personal decision, too. For example one person's idea of a great road might be as mountainous as possible, while someone else is seeking flat prairies or riverside roads.
In terms of display, google maps, mapmyride, ridewithgps, bikeroutetoaster... they all kind of suck, but you can make them do the job if you are patient. I use bikeroutetoaster for making courses to download to my Garmin 705 for shorter routes, but there's no way I would have the patience to do that for a tour.
There are also programs you can buy (Delorme Topo! and StreetAltas for example) that work better, but you do have to buy them and run them on a specific computer, not the www.
Hope that helps at all.