There are a lot of books currently available on chakras, but I found these to be among the best:

Barbara Brennan: Hands of Light

Cyndi Dale: New Chakra Healing - The Revolutionary 32-Center Energy System

Rosalyn Bruyere: Wheels of Light

Martin Brofman: Anything Can Be Healed

Anodea Judith: Chakra Balancing Kit (includes 2 CDs and 7 chakra cards)

and the chakra chapter of Mikio Sankey "Esoteric Acupuncture - Gateway to Expanded Healing" - I would recommend this last book only as advanced reading

Of course choosing a book depend also on how well you like an author, if possible read bits of it before buying the book, just to make sure you like the way the author writes!

Another book which may be helpful is "Gray's Anatomy" or any cheap anatomy atlas. I bought my Gray's Anatomy many years ago while I was a student in London at a books outlet shop for just a few pounds. I could have never imagined I would have used it so much!