It's been really a good experience in learning EJB 3.0 architecture.
Initially I started with Mastering EJB 3.0, the book is good in terms of understanding the concepts with lot of theory.
Some topics are covered in real detail, but it is not enough for JPA and some other topics from exam point of view.
I then switched to EJB 3 in Action just for JPA, because it has about 4 chapters completed dedicated to JPA.
I liked this book in terms of being bit lucid in its explanation. The initial chapters on session and MDBs were also well covered.
Then I purchased Enthuware EJBPlus and gave 1 mock exam, it was an eye opener. Some topics were not covered at all in the books like Exceptions, programming restrictions like operations allowed in beans, APIs suported by Containers, EJB Roles, Interceptors, Persistence Context propogation, Application-managed(JTA & resource-local EM)/Container Managed persistence context in deail etc.
After this, I focussed my learning by strictly sticking to the JSR 220 specs for core and JPA. I read only the chapters that were relevant to the exam objectives.