If you have not yet bought your copy of Expert Oracle Application Express - what are you waiting for? I got my copy in the mail a couple of weeks ago and was thrilled to read it. I am one of those developers who tries to read everything I can on Apex to stay at the top of what I do. And, for me, this book is now a "must read" for anyoune who aspires to be an Apex professional.
This book is written by a collection of authors - most of whom you will know from the forum or from their blogs. What I liked most about the content is that there is a focus on detailed information that you won't find elsewhere. It is not a book for the beginner who knows little about Apex, but rather, is aimed at the professional developer who is keen to know more.
I have already put to use much of what I learned from the book. In particular, Dimitri Gielis's chapter on charts and Martin D'Souza's chapter on dynamic actions really helped to further my understanding on two key areas of importance in my current development. All of the other chapters were also fantastic.
So, if you want to go beyond the boundaries of the basic documentation and move into the world of advanced knowledge - this book is a great place to start. I highly recommend it.