This is just about my most used site, https://www.campgroundreviews.com/. Followed closely by http://www.uscampgrounds.info/.
https://www.campsitephotos.com/ is a good one, but does have limited listings.
And here are some more that I do frequent on occasions:
https://www.campgroundviews.com/?,
https://thedyrt.com/,
Of course, you mentioned, https://www.rvparky.com/,
Another decent search site is http://www.ultimatecampgrounds.com/
This is about the best site for info on a given park, but the listings are limited, https://wxtoad.com/. He does a stellar job on photos.
This is also valuable info, https://www.tripsavvy.com/state-park-entrance-passes-3362306
An amusing site is https://www.roadsideamerica.com/.
And I believe you mentioned Allstays, which has decent info to offer.
This has some interesting info but is a bit awkward to navigate., https://www.fhwa.dot.gov/byways/byways.