I tried EclipseUML today. It was bloody impressive, too. I'm not a big fan of the whole Rational Unified Process or of modeling as a whole, but I do think that UML is a good tool for easy commuication of the relationship between classes.

EclipseUML is so well integrated into the EclipseIDE itself that I found myself reverse engineering packages to understand the classes in them rather than reading the code. Since the diagram browser and the source naviagator are integrated it seems logical to use the UML diagrams as a code-navigation tool – it's quicker to find a sub-class in a diagram than by searching for classes which inherit from something for instance. I've never really seen a tool that does the integration thing so well – MS Visual Modeller doesn't really come close, and Rose/Visio/ArgoUML etc make modelling such a chore I hate to do it.