My favorite would have to be Aquarium Corals by Eric Borneman.
I refer to this book on a weekly basis
Reef Invertabrates is my #2 choice, followed by The Reef Aquarium volume 1 and 2.
Another must have for the library collection is Corals of the World by Dr. Elizabeth M Wood. This book was printed in 1983 and even though it's over 20 years old, this book is full of tons of useful info that that I haven't found in any other book
