One of my favorite online references, Visual Thesaurus, has just been upgraded to version 3, which now includes audio pronunciations, spell checking, and enhanced printing. While it used to be free, it’s still available for a limited number of searches before they require you to pay. Just type in a word, and the visual thesaurus will show a diagram with related words floating around it. Click on one of the other words, and the new word becomes the center of the constellation. It’s quite fun, for word geeks at least, and can be addictive as well.
(hat tip: Josh Rubin: Cool Hunting)