I own quite a few photography books, and
John Shaw's Nature Photography Field Guide is the best. He has some others, which I've also bought. He is both a great author and fantastic photographer.
http://www.amazon.com/Shaws-Nature-P...4863371&sr=8-1
This book is from 2000, and doesn't really talk much about digital photography. Most everything he writes about is still relevant. The camera you use is much less important than how you use it.
Funny, I've heard that said about other things.