JetBrains IntelliJ IDEA
Very good Java (J2SE/J2EE/J2ME) IDE with tons of features and plugins. Have a look to the Early Access Program (EAP)!
IDEA 5.0 (released long ago, 5.1 is coming!) is very good at J2EE, and the JBoss plugin is excellent. Recommend it fully-hearted. NOTE that the jboss plugin does NOT yet support EJB 3.0 deployments...
IDEA 6.0 has been released. It comes now with comprehensive support for EJB3/J2EE5 along with support for all major application servers. With version 6.0.2 JetBrains added support for JBoss Seam with Facelets / JSF...
It's as usual for this incredible IDE: "Develope with pleasure".
IDEA 7.0 has been released. It's even better than 6.0