I’ve recently become addicted to The Visual Thesaurus. It’s easy to use, good fun, and a great tool for branding or naming ideas.
An experiment in language and interface, Plumb Design’s Visual Thesaurus is both an artistic exploration and a tool to explore, study, and analyze the structure of language. By displaying the interrelationships between words and meanings as spatial maps, the Visual Thesaurus translates language into a visible architecture.
Try the Online Edition. (Click on LOOK IT UP to launch the thesaurus window.)

Interesting! Did you buy the app’, Nic? If so, what’s the advantage?
Thanks for the heads up!
I just use the online edition at the moment. I think the main benefits (as I gather from the FAQ) are High-resolution printing, copy & paste, no internet connection (must be faster) and the option to add/subtract words of your own like a personal dictionary. It’s very cheap aswell. I think I will buy it in the near future, but its so easy just to launch the website.
Another beautiful example in the hyperbolic metaphor is ‘valence’, by Benjamin Fry, a graduate of MIT Media Lab. He and Casey Reas wrote the software ‘Processing’ which makes this possible.
See the project description here