The CMU Pronouncing Dictionary
[ http://www.speech.cs.cmu.edu/cgi-bin/cmudict ]
North American English pronunciation site. Pronunciations are machine-read and has over 100,000 words in the database.
[ http://thesaurus.com/ ]
Online thesaurus and dictionary site. Also has a quotes section.
[ http://www.wordcentral.com/ ]
Provides a dictionary and rhyming slang dictionary for students with extra features on subscription.