My online library # 1: Dictionaries

Dictionaries

http://oxforddictionaries.com/ 
One of the best available and most trusted online (Dictionary, better writing, world of games-blog, etc)

http://oaadonline.oxfordlearnersdictionaries.com/
Advanced American Oxford dictionary

http://www.webster-dictionary.org/
Webster's Dictionary / Thesaurus / Medical Dictionary / Legal Dictionary / Dream Dictionary, Spell checker ... more to come!

http://wordreference.com/enpt/ 
English-Portuguese Dictionary

http://wordreference.com/thesaurus/ 
English synonyms 

http://www.wordwebsoftware.com/
 It can be also downloaded 

http://www.ldoceonline.com/  
Longman Dictionary of Contemporary English Online

http://www.urbandictionary.com/
It is a dictionary which contains slangs and many urban expressions. It is continuously updated.