Remember this is a new hobby only like 20 - 30 years or so. In the 80's we thought corals were suppose to be white- LOL. What I'm saying is that a lot of corals have not been identified or you can't get a positive unless they are dead and are able to look at the structure. Sometimes all you are able to get is the family and not even to the genus level. This at first was very hard for me to understand and it still is for that matter. I like to know everything about my livestock. Where it can from, what to feed it, flow, conditions etc. Here is a list of some of the booksI have and the ones I use the most:
I have volumes 1 - 3 of The reef Aquarium by Julian Sprung and J. Charles Delbeek (Wonderful books)
Reef Invertebrates - Calfo and Fenner(Wonderful book - Binding is terrible)
Aquarium Corals ...Eric Borneman (Wonderful book)
Reef Secrets - Alf Facob Nilsen and Svein A. Fossa (OK - I use my other books more).
I have lots more but they are more specialized (Wrasses, clownfish, etc).
The book for corals that I use the most I'd say is the book by Borneman and the Sprung series.
I've been hoping someone would publish a new series like the Veron series. I've been very tempted in purchasing Verons books but I think it was published in the 90's and lots has happened between that release and now. I still might purchase it

. What would be nice I think would be a yearly release of new discoveries. Purchase a series like Verons for a starting point and then have updates to it each year. They do this with freshwater fish (Cichlids, and a few others).