The few that come to mind for me are totally random and very far apart, but my favorites.......so far:
Indian Boundary campground in the Cherokee Nat'l Forest off the Cherohala Skyway on the TN/NC line (kind of between Asheville NC and Knoxville Tn.) - Beautiful wooded sites on a mountain lake. Great place for hiking, biking, kayak/canoeing, etc. No other place like it, it's my go-to for getting away near home.
Topsail Hill Preserve SP, Santa Rosa Beach, Fl (Florida State Parks) - Near Destin Fl. from tents to chromed out class A's, but a beautiful, well kept park with VERY private sites. In no way a parking lot. Tent loop is new and very nice, paved bike trail through the dunes to beach. Great local seafood, etc. but off the beaten path at the same time. Been there for a week in the Fall for 7 or so years now. It never gets old.
Whitney Portal CG - off 395 near Lone Pine, Ca. Perhaps one of the prettiest campgrounds I've ever seen. about halfway up Mt. Whitney. Dizzyingly beautiful, especially to us Easterners, ice-cold rushing creek right through the campground. It's all you can hear.
Princess CG, King's Canyon/Sequoia NP's - at 5900 elevation, on the way in to King's Canyon. Absolutely beautiful place, and kind of spooky because the CG is full of giant Sequoia tree trunks. Neat CG. I will get a site here next visit before I go all the way in to the canyon only to discover full CGs. Don't miss the drive to the end of King's Canyon though. It's highly underrated. Take the hike around Zumwalt meadows at the end of King's Canyon.
Pine Flat, Manzanita, or Cave Spring CGs, Sedona, AZ - just beeeeuuuutiful, and a neat area to discover.
Lizard Creek CG, Grand Teton NP - North of Jackson and the Tetons, just south of Yellowstone. A great spot on the north side of Jackson Lake to stay and explore both parks IMO. Not as busy or big as many of the other Teton CGs.
Fish Creek CG, Glacier NP - ride your bike to Apgar Village and West Glacier. A big CG but nice secluded sites on the lake or creek. Brace for mosquitoes in summer but a stunningly beautiful spot.
If people get fired up about this thread, it could get REALLY lengthy!