This Christmas I got a nifty gift: a piece of software called Visual Thesaurus. I'd been using
the web version but it's a very limited demo. VT draws 3-D clickable maps to illustrate the links between words, clustering groups of related words. It's so much more useful than the straight text list you get in a conventional thesaurus. I've used it to brainstorm about character attributes, to discover title ideas, and just to find that perfect word that I can't quite put my fingers on without help.
The software also comes with a ton of proper names--people and places--linked together, but I haven't tried it. Useful for writers of historical fiction, maybe?
I have no financial interest in boosting this product! I'm just a big fan.