Photoshop CS3 Photographer's Handbook: An Easy Workflow by Brad Hinkel and Steve Laskevitch
This was the textbook used in my digital photography classes. It is an excellent textbook for the level of Photoshop that I am at and continues to be a good resource.
The DAM Book: Digital Asset Management for Photographers by Peter Krogh
I learned of this book in my photography class as well. Despite the fact that it was written for earlier versions of Photoshop and Bridge (and before Lightroom came out), it describes a digital management system that I have found to be most useful for organizing my pictures. (Now, if I only I had the time to actually sort through 10+ years of images)! An excellent resource.
Sierra Club Guide to 35 mm Landscape PhotographySierra Club Guide to Close-Up Photography in Natureboth by Tim Fitzharris
The Art of Photographing Water: Rivers, Lakes, Waterfalls, Streams and Seashores by Cub Kahn
These three books are how-to photography manuals, complete with pictures show examples. Each concentrates on a different area of nature photography.