While I was playing with AXIS today, the tutorial mentioned Eclipse. Eclipse is an open extensible IDE developed by IBM. The project is open source. There's even a OS X version (latest release) available. I downloaded it, but haven't had time to play with it yet. I'll discuss it more later, if its worthwhile. IN the meantime, there's a white paper available that gives and overview.
One thing I am aware of is that Eclipse will perform some of the same functions as Xdoclet in preparing EJBs. Xdoclet is for those of us who like command lines, emacs, and build tools like ant. IDEs are for GUI types. Take your pick.