AllWords.com English dictionary with multiple-language translations.
Dictionary.com Multi-source dictionary search service.
howjsay.com An online English pronouncing dictionary with instant sound.
Merriam-Webster Online This online dictionary and thesaurus for English includes audio pronunciations.
OneLook Dictionaries A search engine for words and phrases, and reverse dictionary feature for when you don't know what the word is, but you can give a definition.
Reverse Dictionary Useful when you know what you mean but can't find the exact word! Type a concept into the search engine and receive a list of words related to it.
Rhyme Zone An online rhyming dictionary.
The Visual Dictionary Visual learners will appreciate this resource which identifies the names of parts for hundreds of items and beings in the broad categories of animals, plants, the human body, music, transportation and clothing.
Wordsmyth Dictionary with a complete, integrated thesaurus. Some features require registration.
YourDictionary.com More than 2500 dictionaries and grammars in over 300 languages, games that build language skills.