I put some pics not long ago of the current state of Hampton Down. Looks on the OS like it's in the middle of a field but just stay on the track till you come to the info board.
Kingston Russell is cool, and was nicely mown when we were there. Maumbury Rings is impressive but may well be full of annoying sixteen year olds. Go in the morning while they're still in bed...
Monkey World is ace. Also check Prince Charles' Disney-Britain-Enid Blyton-Utopia Poundbury on the edge of Dorechester. Wierd...