http://dictionary.babylon.com Many categories, Language, Translator, Thesaurus
http://dictionary.cambridge.org Idioms, Phrasal verbs, Audio pronunciation
www.merriam-webster.com Dictionary, Thesaurus, Medical, Spanish-English
www.onelook.com Reverse Dictionary
www.askoxford.com Quotations, First Name Dictionary, Ask expert, Writing help
http://dictionary.reference.com Dictionary, Encyclopedia, Word games, Crossword solver
www.specialist-online-dictionary.com Computer, Scientific, Legal, Political, Philosophical, Music, Misc
www.yourdictionary.com Grammar Rules & Usage, Industry specific dictionaries
MEDICAL DICTIONARY
www.medical-dictionary.thefreedictionary.com Medical conditions, Medications, Anatomical terms, amd more
LAW DICTIONARY
http://dictionary.law.com Legal terms, Definitions, ABC list
THESAURUS
http://thesaurus.reference.com Dictionary, Encyclopedia, Translator

Dictionaries

Translators

http://translate.reference.com Ask.com translator – over 50 languages
http://babelfish.yahoo.com/ Yahoo Babel Fish Translator

Synonyms

Quotes:

A synonym is a word you use when you can’t spell the first word correctly.
Burt Bacharach

An antonym is the opposite of the word you’re trying to think of.
Unknown
Definitions:

Synonym: A word having the same or almost the same meaning as another word.

Antonym: A word having the opposite meaning of another word.

Resources:

www.thesaurus.com Includes word games, tools, and resources
www.synonym.com/synonyms Enter words A-Z for synonyms, antonyms and definitions.
www.synonyms.net Synonyms, antonyms, and thesaurus
www.pbskids.org/lions/games/synsam.html Interactive games for kids

Quotes

www.quotationspage.com Quotations by authors (3,100), by subject (247)
www.quoteland.com/ Quotations by author, topic, art, dreams, love, sports, library
http://quotations.about.com/ Quotes: love, funny, wedding, short, Chinese, birthday, movie/TV, friendship, poems, spiritual, Shakespeare, business, holiday
http://theotherpages.org/quote.html Contains approximately 28,966 entries, and the Alpha by Topic is the best place to start.
http://www.citatum.org Categorized Quotes.