I am currently working in an Oracle Apex development team at Philips in Eindhoven. Two colleagues of our team have been writing for almost a half year on their first book.
Marcel van der Plas and Michel van Zoest have produced a real good book with over 80 great recipes to develop and deploy fast, secure, and modern web applications with Oracle Application Express 4.0. After reading this book, you will be able to create feature-rich web applications in Application Express 4.0 with ease and confidence.
This book is a practical reference guide for every APEX developer and is available as paperback or as e-book: https://www.packtpub.com/oracle-apex-4-0-cookbook/book.