I know you said "book" but here's 4 from a novice prospective.

1) "Acitve Nymphin" by Rich Osthoff. Since I see so little surface action on my home river, the Pigeon (NE Indiana), I'd better try going deep.
2) "Nymph fishing for Larger Trout" by Brooks. Who can resist "LARGER Trout." So again, I'd better go deep.
3) "Presenting the Fly" by Lefty Kreh. A great coffee table book with good information.
4) "Fly fishing for Dummies" by Kaminsky. When you are a newbe, like me, its a great general reference.

All came from internet book stores like Alibris (so were cheap) and were in great condition.

Enjoy!

Joe