How's this for an interesting web tool? WikiMindMap (http://www.wikimindmap.org/) allows you to create mind maps of Wikipedia entries. Here's a sample of what it created for the word "brainstorm."
Besides English, it searches ten other languages. It allows you to bring any word from an individual branch to the centre for additional mind maps. By double-clicking any word, it links directly to the specific Wikipedia entry.
Yeah, yeah - I know all the bad things about Wikipedia. (Read: Don't send me e-mails how horrible it is.) And, some of the mind maps I created had a few odd suggestions. When I typed in "ideas," it included "hamsters." Perhaps because a hamsters' superfamily is "Miroidea"? As my Grandma used to say, "The mind reels."
Still, a great addition for brainstorming! Enjoy!