YLB

Oxford Dictionaries Online - English Dictionary and Thesaurus

http://oxforddictionaries.com

Oxford Dictionaries Online - English Dictionary and Thesaurus

Big Huge Thesaurus: Synonyms, antonyms, and rhymes (oh my!)

http://words.bighugelabs.com/

(Also blog post ideas and story plot/logline resources for writers.)

Visual Dictionary Online

http://visual.merriam-webster.com/

Visual Dictionary Online

VocabGrabber : Thinkmap Visual Thesaurus

http://www.visualthesaurus.com/vocabgrabber/

VocabGrabber : Thinkmap Visual Thesaurus

Welcome | Wordnik

http://www.wordnik.com/

An ongoing project devoted to discovering all the words and everything about themMore than 1.7 million words, and more than 130 million examples!

The Internet Picture Dictionary

Free online Dictionary of English Pronunciation - Pronounce English words correctly

http://www.howjsay.com/

Free online Dictionary of English Pronunciation - Pronounce English words correctly

Oxford English Dictionary: The definitive record of the English language

http://www.oed.com/

Oxford English Dictionary: The definitive record of the English language

Dictionary.com

Thesaurus

Thesaurus are excellent tools to use when you are looking for words with the same or similar meaning (synonyms). 

Webster's Online Dictionary - with Multilingual Thesaurus Translation

Visuwords™ online graphical dictionary and thesaurus

Dictionary and Thesaurus - Merriam-Webster Online

Thesaurus.com

Denshi Jisho - Online Japanese dictionary

http://jisho.org/

Denshi Jisho - Online Japanese dictionary

Dicionário Português-Inglês WordReference.com