Dictionaries
English-Greek dictionaries:
http://www.ectaco.co.uk/English-Greek-Dictionary/
http://www.wordreference.com/engr/dictionary
http://oald8.oxfordlearnersdictionaries.com/ : Dictionary with pronunciation
http://photographicdictionary.com/ : Dictionary with photos
http://www.etymonline.com/: Etymological dictionary
http://www.languageguide.org/english/: Practice English vocabulary, the alphabet and numbers. Place your cursor over an image or text to hear it pronounced aloud.
Reading
http://mrnussbaum.com/readingpassageindex/: reading passages with comprehension questions.
Games
http://learnenglishkids.britishcouncil.org/en/kids-games
http://gamestolearnenglish.com/
http://ts.sch.gr/repo/online-packages/dim-anglika-d-e/d17/cd/startup.html

