EJB Design Patterns (published March 2002)
Consists of 20 EJB-specific patterns written a style similar to AlexandrianForm. The book is 'lower level' than most patterns books, in that it is intented to cover EJB-specific implementation and design issues.
The book also contains:
Available online at: http://www.theserverside.com/books/EJBDesignPatterns/index.jsp
Although you do have to be a member of TheServerSide to download it.
This isn't so much a book of DesignPatterns as idioms and best practices. Much of the material is concerned with architectural principles and workarounds to bugs rather than describing patterns. The RuleOfThree isn't really adhered to, largely because it's hard to find examples of enterprise applications with available source code, which makes the entire book seem very theoretical. Fowler's PatternsOfEnterpriseApplicationArchitecture suffers from the same problem.