TheServerSide.com have a book review of a book called ‘Covert Java’, which covers topics such as decompilation, JVM internals, debugging, and tracing.
These are topics which are not covered in many other books – some good reading for someone with a couple of years Java experience and wants to increase their understanding of the Java platform, although maybe not as much use for someone with more than a couple of years experience and has probably already used these techniques.