I don't know of any Java 6 cert exam study guides, that exam is so new.
The Java 6 equivalent of the book I've used has an anticipated publish date of mid-July, and that will probably slip.
http://www.amazon.com/SCJP-Certified-Programmer-Java-310-065/dp/0071591060/ref=sr_1_7?ie=UTF8&s=books&qid=1204233825&sr=1-7This is SCJP 5 book I've used, and the one we use in the breakout:
http://www.amazon.com/Certified-Programmer-310-055-Certification-Guides/dp/0072253606