Marc is considering Eclipse. He makes some criticism by comparing it with IntelliJ IDEA. I never tried it, but it seems to be the only real competitor to Eclipse, as people complaining about Eclipse are mostly IDEA users. Every other people trying Eclipse (including me) quickly become addicted to its nice features.
Yes, Eclipse currently lacks a good XML editor, but considering the number of plugins that tackle this problem, this shouldn't be true for long.
There's also TogetherSoft's ControlCenter, which has top-cool UML features, but this is a resource hog (better have lots of memory) and I've been told it's rather expensive, while the free version of Omondo's Eclipse plugin provides class diagrams, which is what a Java developer uses most often.
Omondo's price list also shows that the Enterprise Edition (the most featured version) will be free for non-profit organizations, defined as ".org company". Does this mean we can use it for Apache projects ?