JetBrains has posted the first release candidate of Intellij IDEA 4.0 (registration required). IDEA is a $699 payware integrated development environment for Java that's been getting a lot of good buzz for the last year or so. New features in 4.0 include a GUI designer, CVS integration, the ability to modify code from within the debugger and continue running, generics support, and JUnit integration.
Personally, I'm an Eclipse person after a horrid initial experience with IntelliJ about a year and half ago. Perhaps it's improved since then. A lot of people I respect are raving about IDEA. However, Mac developers I hear from about IDEA 4.0 are distinctly negative about it, which is always a a bad sign, as they're usually the only ones who actually understand user interfaces. If the Mac programmers don't like your product, that normally means there's something wrong with it.