Eclipse
Features in Eclipse itself
I've just started using Eclipse for the sake of the folding editor and plug-ins. Wish there were a plug-in for previewing CSS, though there is a simple CSS editor plug-in.
Sysdeo Tomcat plugin
Eclipse-wise, just being able to start and stop Tomcat from a GUI rather than from multiple DOS windows is a delight.
Eclipse Web Toolkit Project
For those using Eclipse, the Eclipse Web Toolkit Project looks very promising, though it is currently a bit rough around the edges. Moving forward with JSR-168 and alternate view technologies like JSP/JSTL, integrated refactoring tools for both Java and presentation code sounds wonderful.