The following links may be of interest:-

Dr Sandy Gerrard's site on roundhouses.
Alan Endacotts site, which gives information on the Sittaford Tor circle discovery and the Northern Moor.
Information on Stonehenge. 
Dave Parks' excellent website, which provides more descriptions of the sites than I provide.
And his Dartmoor Cairns and Cists
The English Heritage PastScape database. 
Devon Archaeological Society 
The Devonshire Association 
Plymouth and District Archaeological Society 
ACE Archaeology 
Dartmoor National Park Authority 
Legendary Dartmoor 
Megalithic Mysteries 
Megalithic Walks 
Dartmoor Walks Relics
Britain Express 
The Megalithic Portal 
Stone Circles 
The Dartmoor Archive
Divine Dartmoor Walks
The Dartmoor Resource
Dartmoor Walks Index
Liz Miall's walks