Adventure Cycling
As a fan of touring, I have spent hours searching for bike routes throughout the country. For long distance rides, www.adventurecycling.org has to be the best place for detailed maps. They give you the distance between turns, what amenities are located in each town that you are biking through, and for the most part keep you on roads that aren’t overly crowded with cars. Sometimes they take you a bit out of the way but they tell you that on the map. In addition to the detailed maps, their website offers advice, gear, and a way to join other cyclist looking to tour.