Hiya Bellybones
get yourself a copy of A Guide to the Stone Circles of Britain Ireland and Brittany.
ISBN 0-300-06331-8
It'll cost you about ten British Pounds, is readily available and is slightly bigger than your arse pocket so fits snugly into your bag, glove box or where ever. As a field guide to Stone Circles it just can't be beaten and is probably used by most of the regular contributors here.
http://www.amazon.co.uk/gp/reader/0300063318/ref=sib_dp_pt/026-1843341-5976463#reader-link
cheers
fitz