This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
According to that, the O'Reilly Enterprise JavaBeans 3.1 is the best book. I believe the Head First EJB is for the EJB2.0 specification; however, it is still a good book for describing EJBs if you are not familiar with them.