We alternate Trailer Life & Woodall's (Buy one new yearly, hang on to old one, transfer margin notes to all new directories) and we like Wright's Free Campgrounds (Eastern Edition hopefully new book will make it out this year). I use the internet alot and keep a "personal" directory of campgrounds that we like and note special requirements (best site, etc).
http://www.rvparkreviews.com is wonderful when a park is listed. We have never used Frommer's but I think they prefer "resorts" and we prefer public campgrounds. You will need to just try them to see what you like. We have found the rating systems to be subjective. The factual info regarding amnities and website addresses help alot. Just remember that pictures can be deceving. Websites sometimes list the current rates and sometimes lists their restrictions. Usually the driving directions are pretty good.