I use Together very often, and it is a very powerful tool.
It will reverse engineer your code, and generate both class and interaction diagrams for you. In addition, it works directly on your codebase (there is no 'import'). There are some features for generating documentation, either via JavaDoc or
word templates.
As Ilja says - this does not replace (although it can form part of) good documentation. You will still have to spend some time reworking key diagrams and writing some supporting notes, but Together makes this all very easy.
I would strongly recommend taking a look at this - I prefer it to Rose, but everyone has their own preferences.
regards,
paul.
