Learn Photoshop in a Nutshell - Graphics & Design
Defining and describing every tool, command, palette, and sub-menu in Photoshop 4, this guide contains unique nine-graphic grids that show the effect of different command settings on a single image--eliminating unnecessary work and saving time. This book helped me to get the basics of Photoshop, very easy to follow. Even though it is not for the most current version, it still is very helpful and you can still get alot of info from this book.
Actually this book teaches you to make informed choices as you work, eliminating time spent searching for just the right combination of filters and effects and reducing the risk of incorrect editing decisions. I have found this book an invaluable guide.