http://www.visualthesaurus.com/From the site: "The Visual Thesaurus isn't just a fun way to avoid writing. Sure you can surf our word maps, discover new meanings and suss out relationships between words. But at some point you gotta put quill to parchment, pen to paper, keyboard to file. You got to get to work. That's where the Visual Thesaurus really comes in handy. With over 145,000 words and related meanings, all connected by a remarkable interactive interface, you'll find the right word, master usage -- and use words more precisely. The best part is the Visual Thesaurus works naturally and intuitively like your brain, not some paper-bound book. So you'll get your writing done. And still have fun."
You can buy the software for $40 or a year's subscription for $20. What I like about this thesaurus (aside from a lot more word connections than the usual thesaurus) is that it's easy to get precise word selections and go diving for words when all you can think of at the time is a word related to it (such as maybe trying to find "Formica" but only being able to think of "plastic").