"Gang of Four" was the original and is still the touch-stone for OO
patterns. It uses smalltalk code in the examples. "Head first Design
Patterns" is a java-centric interpretation of the GOF list so it's
probably more relevant.
There are HEAPS of enterprise pattern books but they seem to go out-of-
date as quick as they are printed.
If anyone else in the group has a recommendation then stick it in the
resources page - http://groups.google.com/group/bristoljug/web/java-resources?hl=en