EclipseUML. An UML plugin for Eclipse [Java-Channel]
This all looks pretty groovy. It sounds like they've also got an interesting business model - I just hope the free version keeps usable.
NOTE that it doesn't currently work for Eclipse 2.0.1. It appears to depend on com.ibm.etools.gef rather than org.eclipse.gef - so its probably worth waiting for another version. I even hacked the plugin.xml to fix this error and it still doesn't work. So its one to come back to later when it actually works!
Though I'd really love an open source Maven plugin that could auto-generate some UML views of the code as part of the build process, which could be customized according to some pattern matching.
Autogenerating full UML models (even on a package basis) are often a bit noisy - I don't wanna see every class, method and attribute in each package - I'd rather filter a few things. So I'd much rather something like...
<diagram name="overview style="class">
<includeClasses name="Foo, Bar, *Factory">
<includeMethods name="create*, add*, remove*"/>