Inline UML in your java code
PlantUML is a nice alternative to using a diagram based modeler. It allows you to put UML and interaction details within the comments of your code. And as you navigate the class files in eclipse it displays the diagram associated with the class within the plantuml view. It also has a doclet that allows you to build the images and documentation from ant.
This approach is quite nice allowing for the documentation to be within the context of the work that is being done.