http://richthegeek.github.com/coffeegraph/
Instructions: use the toolbar, select "Wizards" and choose an option. Any number of nodes > ~800 will be slow, and I'd recommend using only a modern browser.
What's unique about this project? Well apart from being quite polished (I think) it's also got some heavy work into the Kamada Kawai algorithm - it uses a simplified BFS for APSP (cutting pre-run times by ~95%) and is the only KK algorithm I know of to work in 3D (correct me if I'm wrong).
Full source is available: https://github.com/richthegeek/coffeegraph
Boring write-up also: http://richardlyon.co.uk/dissertation_draft1.pdf
Let me know what you think!