Here's a few of my favorites
"The Reef Aquarium" Volumes 1-3 by J. Charles Delbeek and Julian Sprung.
"Natural Reef Aquariums" by John H. Tullock.
"Reef Secrets" by Alf Jacob Nilson and Svein A. Fossa.
"The Conscientious Marine Aquarist" by Robert M. Fenner
These books are expensive but well worth it and you can find them used at amazon.com. Also Check out nano-reef.com and reefcentral.com they both have some great forums and are real helpful at answering questions.
Merlin