Welcome!

Try the Shire Archaeology series as an opener, introductions by some fairly heavyweight authors:

http://www.amazon.co.uk/Megalithic-Tombs-Barrows-Britain-Archaeology/dp/0747803412/ref=sr_1_7?ie=UTF8&s=books&qid=1205763947&sr=8-7

http://www.amazon.co.uk/Prehistoric-Henges-Shire-Archaeology-Aubrey/dp/0747801231/ref=sr_1_12?ie=UTF8&s=books&qid=1205763947&sr=8-12

http://www.amazon.co.uk/Irish-Megalithic-Tombs-Shire-Archaeology/dp/0747805989/ref=sr_1_38?ie=UTF8&s=books&qid=1205764006&sr=8-38

http://www.amazon.co.uk/Prehistoric-Astronomy-Ritual-Shire-Archaeology/dp/0747806144/ref=sr_1_48?ie=UTF8&s=books&qid=1205764006&sr=8-48

http://www.amazon.co.uk/Prehistoric-Stone-Circles-Shire-Archaeology/dp/0852639627/ref=sr_1_14?ie=UTF8&s=books&qid=1205764062&sr=8-14

Not sure how up to date they are, but they're a good start. The just dive into some proper Aubrey Burl and take it from there...