Inspired greatly by Gregor and Erik's great talk at TSSJS 2006 we've started to add some visualisation plugins into Apache ActiveMQ.
There is a <destinationDotFilePlugin/> broker plugin which generates a DOT file such as this example whenever a destination is created or destroyed in the broker. You can then turn this dot file into a nicely rendered image such as the one below.
If you are using OS X then you can open the DOT file using graphviz which will then automatically re-render if it changes, so you end up with a real time graphical representation of the topic and queue hierarchies.
Also if you want to edit the layout a little before adding it to a wiki to distribute to your team, open the DOT file with OmniGraffle then just edit away
There are so many different things we could visualise; our only limitation is our imagination. So if you have any ideas for what we could visualise please add something to our Visualisation Wish List