Hi Brownie and welcome.

The Shire series of books are an excellent and cheap starting point.
Many years ago I bought a book which was titled something along the lines of A-Z of Archaeological Sites of Britain. This had a good description of sites around the country and how to get there including grid ref's. Unfotunately I think I left it on the top of my car when I drove off once and never saw it again. I have since bought a similar book which is a bit dated now but still useful (useful if you live in England that is) called Guide to Prehistoric England but it has less photo's .
I recommend a good map of your local area such as the OS Explorer series and getting out and visiting sites near you. There is nothing like seeing places first hand to get a grasp on the different barrows, henges and circles.
Where you live will dictate what you what you have locally and of course this site has a very good map of what you can find near you along with other peoples experiences of them.

Good hunting

:o)

Scubi