If you're studying for the OCA, our book (K&B 6), should give you pretty good coverage. If you study the following chapters from K&B 6 you should be in pretty good shape for the OCA:
chaps: 1, 2, 3, 4, and 5
chap 6 - the String and StringBuilder sections
chap 7 - the hashCode() and equals() sections, and only the ArrayList class.
The chapters (and sections) listed above ARE NOT a perfect overview of everything you might encounter on the real exam, but I'd say they represent a 95% overlap. We'll be nailing down that last 5% over the next several weeks.
Someone knows what's the others 5%?