There are a couple of other sites--can't remember if you have to buy the hard copy to use them or not: Woodalls and Trailer Life.
I'm a relative newbie and would recommend you invest in the hard copy of Woodalls. I think of it as the "bible" of campgrounds and parks. This year you can get a West version and an East version, and I suppose you can still get the "entire continent" version. I bought this year's west version to replace my two year-old entire continent version.
Ciao,
Doug