Barry Boone 1.1 is good. It helped me significantly for the Java 2 exam. But I would also recommend:
The Complete Java 2 Certification Study Guide by Simon Roberts, et al (Hardcover - July 1999)
Amazon.com Price: $34.99
Java 2 (Exam Cram) by Bill Brogden, William B. Brogden (Paperback )
Amazon.com Price: $23.99
I really don't think you'd need anything more. Sure,
you should also take good mock exams available for free on the Web. And if you have a lot of money, you could buy the commercially available preparation tools.
We have both types of tools listed here in
http://www.javaranch.com/mock.html