X2 on Lone Rock CG being nice.....as long as you are looking for dispersion camping.
The Nat. Park CG at Lee's Ferry is nice (and there is a free dump station nearby)
Horseshoe Bend is OK I guess. But if you go down to Lees Ferry, you can get a boat ride up to the dam (it's called a "backhaul") where you can put your own kayaks (if you have them) in and then float downstream, right through Horseshoe Bend, back to Lee's Ferry. Stop in at Marble Cyn Lodge to arrange this. Also, when you cross the bridge (Navajo Bridge), there is a visitor center. Condors are often seen under the bridge there.
About 20 miles West of Marble Canyon is a gravel road called House Rock Valley Road that goes north. A couple miles North on this road takes you to a Condor Viewing area. You will need binoculars (or a spotting scope) and patience, but you'll probably see condors. If you have a solid four wheel drive vehicle, you can check out White Pocket a little further up HRVR. Looks like The Wave....without the "impossible to get" permit required. Deep sand out there so be careful. There are tour companies that will take you out there from Page if you prefer to not tempt fate. A bit further north on HRVR (about 5 miles past the turn off's for White Pocket) is a cool pictograph panel. Large parking area so you can't miss it, then it's only about a 3/4 mile hike on an easy trail starting on the other side of the road.
Behind (on the N. Side) of Lake Powell is pretty neat (and very remote) too.
You could easily spend a life time there and not scratch the surface.
Have fun,