Urban Dictionary - Urban Dictionary is a Web-based dictionary of slang words and phrases.
Forvo - Forvo: the largest word pronunciation dictionary in the world, now with translations.
Reverse Dictionary - Describe a concept and get back a list of words
Howjsay - Pronounce words correctly with the world’s largest English pronouncing dictionary.
Dictionary Anywhere - Dictionary Anywhere is an open-source and easy-to-use browser extension for Mozilla Firefox and Google Chrome that allows you to check definitions easily while browsing the web.
Shtooka - The Shtooka Project is a multilingual database of audio recordings of words and sentences.