My books on the SW revolve around hiking and biking trails, rather than camping itself. A little out of the SW, but one book that you might like is "Colorado Campgrounds: The 100 Best and All the Rest". Sure it describes the popular CG's, but also lists quite a few others. One of the sections on each campground describes the popularity of that CG so you can balance the scenic attributes and CG's facilities with the popularity and privacy of the CG.
You might also check out the books by Moon such as
this one for Utah. I find the whole Moon series to be quite helpful in my travels, not just for CG's but lesser known sights to see and places to eat. Check with you local library to see if they have any of the Moon books on hand so you can see what they are like before ordering one.
Another vote, though, for the
Desert USA website to help with your trip planning. Maybe start there to find out about the lesser know destinations and then research your camping options from there. For that, I use this
Campground Map. Just input the name of the closest town and the map will zoom in showing most of the public and private campground options.