Anagram Generator
Probably not very useful to poets, but fun anyway. Enter a single word or list of words, specify the minimum number of letters for a word match, and the program will create a list of anagrams.

The Book of Cliches
Collection of cliches and common expressions organized by general subject matter.

Cliche Finder
Searchable database of over 3,300 cliches. Also has some interesting information on what makes a cliche and links to related sites.

Dictionary of Phrase and Fable
Searchable hypertext edition of the 1894 work by E. Cobham Brewer.

Looksmart's Directory of Online Encyclopedias
Why duplicate what's already been done well? :-)

Research-It!
A wide variety of resources useful to writers, all on one page: standard dictionary, rhyming dictionary, thesaurus, translator, anagrams, acronyms, quotations, and much more.