Besides all those mentioned, I also will do a Google search for RV Parks, by city and sometimes state.
One of 'my' better searches is with Microsoft Live Maps
When on the site, type in the city you wish to view in the "Live Search" pane. Once it comes up, type RV Park in the Live search pane. It will pop up CG's in the Center of the map. You can then drag the map and the CG will re-populate.
No one piece of information sources is all-inclusive, including the books. I use all sources until I find a place to stay. And yes, sometimes I'm across the street of a better place, but hey, I can move.
The only reviews I believe in are the ones I have written. All others are taken like a grain of salt.
Once a CG is located, a Google search on that CG will typically give you a web page that may have the current rate, but it is always a good idea to call.
Call ahead and tell them what discount you would like to use. The CG's normally set aside a percentage of their CG for discount holders. If they say they are full, ask if they have any non-discount sites. You may find that they do, and don't haggle over discount/non-discount. Many others have been rude to the CG staff when the arrive and find out that they are "full" to see empty sites. It has cut off discounts at many CG's.
Not singling any one out, but just generalizations.
Remember, books are extra weight and storage.