ACA has mapped specific routes over the past 38 years and developed what we call the Adventure Cycling Route Network. There are groups, state and local agencies and regional organizations that also have developed/are developing bike routes, for example the East Coast Greenway and the Mississippi River Trail, Inc. And the Rails to Trails Conservancy had helped get numerous railroads beds converted to trails. We don't see these trails, and others like the GAP and C&O as a part of our AC Route Network. They certainly add to the overall choices where one can go on a bike, and we're happy to talk about them. We even use them on some of our tours. Many of these trails already have online maps or guidebooks. John is correct is saying that we try to stretch our resources instead of duplicating what is already available.
As far as I know, there isn't an online site or organization that lists all the different bike routes and trails all over the country.