This list is of the website that are generally my "go to" for finding a campground (outside all of our memberships).
AllStays.com: In additional to a site full of good directory information, they have nice Apps. Allstays are my "go to" when we travel. This site is great for finding Truck Stops, Wal-Mart, Sam's etc, Rest Areas and yes... it will help find campsites. This site allow multiple sorting options to narrow your search. I like being able to sort by price, amenities and so much more.
RV Parky.com: This is another resource that can be used to find RV Parks and campgrounds. It is an interactive map that will show Campgrounds, Rest Areas, Wal-Marts and much more. It is additional tool to have in the campsite search "toolbox".
UltimateCampgrounds.com: This is a resource I use when trying to stay at any kind of government camping area. It will provide information on US and Canada public campgrounds. It is a One-Stop resource for Corp of Engineers, BLM, National Parks, State Parks and So Much More. There is a small fee for the Ultimate Campgrounds App; but I think it is well worth it.
Freecampsites.net: This site shows campsites that other RVers have found. A map displays possible "free" camping area. This can be Wal-Mart, Cabela's or public land.