Reverse Dictionary - Describe a concept and get back a list of words
Urban Dictionary - Urban Dictionary is a Web-based dictionary of slang words and phrases.
Silicon Valley Dictionary - Urban dictionary meets Silicon Valley
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.
FoxType Thesaurus - Visualize similar words for _____
SlangSite.com - SlangSite.