Students
Dictionary that includes sentence examples, related phrasals and audio
http://www.merriam-webster.com/
A free online Talking Dictionary of English Pronunciation
A dictionary with Sentence Examples
http://sentence.yourdictionary.com/
Quizzes and games for advanced students
http://www.merriam-webster.com/game/index.htm
Reading tests
http://www.move-on.org.uk/practicetests.asp
Grammar practice for all levels
http://elt.oup.com/student/headway/?cc=global&selLanguage=en
Teachers
Free worksheets galore.
Web 2.0 tools
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