Hi Megadread,
For lonely stone circles I'd recommend the Burnmoor complex, bleak and beautiful, and you could camp up there, with Scafell, the second highest mountain in England above. Good campsites and pubs exist in Eskdale.
For a sheer wow factor, well, it has to be the Pike of Stickle stone axe factory, although great care is required to reach it, as the ground is very steep and loose, and disturbance must be avoided. There is a National Trust campsite at the head of Great Langdale, although you could camp on the tops, and a fantastic boozer in the Old Dungeon Ghyll. Copt Howe rock art is nearby.
For all sites check out the nearby facilities on the links.
The usual sites will have a lot of visitors at this time of year (school hols).
Have a good 'un, wherever you go,
TE.