Wolfram|Alpha is a great resource for writers. It has an enormous words and linguistics database that writers can use for such things as word definitions, origins, synonyms, hyphenation, and Soundex lookups.

Type “word contest”, and Wolfram|Alpha will retrieve the word data for the English word “contest”. The results tell you many definitions of the word, that its first known recorded use was in 1603, that it rhymes with “conquest”, and a wealth of other data on just that word.

Excellent if you're stuck for ideas. I just entered "word clever", and the network synonym map at the bottom of the page is wonderful. Try it yourself -- I'll bet you couldn't get from "clever" to "chicane" without this tool.