The GOF (Gang of Four, aka. Gamma et al., "Design Patterns") book on patterns is
the book about patterns. Though written for C++ and Smalltalk, it is a standard.
Once upon a time downloaded a copy of Cooper's book. But the Java samples did not really help me to understand how the patterns are supposed to work.
I ended up with buying the GOF book (although I'm unfamilier with C++, and do not know Smalltalk). However, there is nothing comparable out there, the GOF book is kind of a must have for any serious developer. The examples just happened to be written in C++ / Smalltalk - the rest of the book is also understandable to Java folks.
Secondly, the GOF book describes 23 basic patterns. Some of them have found way into the Java language itself.
A good resource for patterns and Java is
http://www.javaworld.com. They have articles on a regular basis, covering all kinds of patterns, including the GOF ones.
[ April 30, 2002: Message edited by: Mag Hoehme ]