AlphaDictionary - http://www.alphadictionary.com
A free online English dictionary, dictionaries and grammars for 350 languages.
Cambridge Dictionaries Online - http://dictionary.cambridge.org/
Publishes a selection of English dictionaries for learners worldwide. Also offers tools, resources, word of the day and blog.
Collins Dictionaries - http://www.collinsdictionary.com/
The official online dictionary from Collins with over 1 million entries.
Creativeglossary.com - http://creativeglossary.com/
A regularly up-dated collection of creative terms.
Dictionary Link - http://www.dictionarylink.com/
Your guide to free online dictionary and translation services.
Dictionary.com - http://dictionary.reference.com/
Find accurate definitions and audio pronunciations of words.
Free Dictionary - http://www.freedictionary.org/
An online English dictionary that gives you English definitions, synonyms, pronunciation, spelling and more.
HyperDic - http://www.hyperdic.net/
A hyper-dictionary of English, Spanish and Catalan language. Also features downloads, and help.
Pseudodictionary.com - http://www.pseudodictionary.com/
The place where words you've made up can become part of an online dictionary.
Visuwords - http://www.visuwords.com/
Online graphical dictionary and thesaurus to find their meanings and associations with other words and concepts.