Well, there are a number of core references. As you may be aware, Oracle would like to see these exams take some of their cues from one or more of the courses they list as a prerequisite to taking the exam, whether you take all those courses or not. I don't have that list in front of me but it includes
Architect Enterprise Applications with Java EE
Java Design Patterns
there are other advertised courses that satisfy the exam requirement but are not as valuable, in my view, for exam prep
Java Design Patterns (which I wrote) takes most of its EE-oriented material from Adam Bien's Java EE Patterns and Kent Beck's Implementation Patterns. I'd read Bien's book carefully before plunging into this exam. Hint, hint.
The most helpful document, though, will be the exam objectives map. I don't know when Oracle plans to publish it of if they already have, but you really want to look that over before diving in.
Hope this helps,