Learner's Dictionaries
 

•  Cambridge Advanced Learner's Dictionary
   

• Oxford Advanced Learner's Dictionary  (OALD_
   

• Longman Dictionary of Contemporary English (LDOCE)
   

• Merriam-Webster's Learner's English Dictionary with Audio Pronunciations
   

• Merriam Webster's Unabridged Dictionary (AmE)
   

•  The Online Etymology Dictionary

 

English Pronouncing Dictionaries

•  A Free Online Talking Dictionary of English Pronunciation

• All the words in the world. Pronounced
  
  Picture Dictionaries

• Merriam Webster's Visual Dictionary Online (AmE)

• The Visual Dictionary - Flora, Fauna, The Human Body, Music, Transport & Clothing

• The Internet Picture Dictionary

 

English Glossaries, Thesauruses

• Roget's Thesaurus

• A Dictionary of English Slang and Colloquialisms in the UK

• Urban Dictionary - An amateur dictionary of contemporary English slang terms from urban cultures and subcultures

• The Devil's Dictionary

• WordNet Thesaurus Online

• Visuwords - Online Graphical Dictionary