The Michelin North American Road Atlas 2010 is the most complete spiral bound atlas I've found.
http://www.amazon.com/gp/product/2067143131/ref=oh_aui_search_detailpage?ie=UTF8&psc=1I've ordered about a dozen different atlas's off Amazon and compared them. This was the most complete and showed the most secondary roads. The best part was it showed all campgrounds!! No matter where I was, I knew if there was a camp ground available if I continued in the direction I was headed or where one would be near by. Also how many campgrounds.
For example; I was traveling between Tiger, WA and Colville, WA on Hwy20 (294). It was about 4pm and I wanted to find a spot for the night. This map showed me there were 3.