A2 - B1 levels

•  English Grammar in Use Book with Answers, Cambridge University Press, Fifth Edition.
  Autore: Murphy.  ISBN: 9781108457651
• English Vocabulary in Use Pre-Intermediate and Intermediate with Answers. Cambridge University Press, Fourth Edition. Autore: Redman. ISBN: 9781316631713

B2 levels

• Language Practice for B2 First, Hueber Verlag GmbH. Author: Vince, M. ISBN: 9783192516733
• English Vocabulary in Use Upper-intermediate & Advanced, Cambridge University Press. Fourth Edition. Authors: McCarthy, M.; O’Dell, F. ISBN: 9781316631744

C1-C2 levels

• Language Practice for C1 Advanced, Hueber Verlag. Author: Vince, M.. ISBN: 9783191626730
• English Vocabulary in Use Advanced. Authors: McCarthy, M. & O’Dell, F., 3rd Edition. Cambridge University Press. ISBN: 9783125410244
• Advanced English Grammar in Use Firth Edition. Author: Hewings, M. Cambridge University Press. ISBN: 9781108920216

http://www.oxfordlearnersdictionaries.com
https://dictionary.cambridge.org/dictionary/english/  
https://dictionary.cambridge.org/it/dizionario/learner-inglese/ (A2 and B1 level) 
http://www.merriam-webster.com/ (Advanced, US English)

Some of the following sites are available in both English and Italian:

https://www.britishcouncil.it/esami/ielts
http://www.cambridgeenglish.org/exams/
http://www.cambridgeenglish.org/learning-english/exam-preparation/
http://www.toeflgoanywhere.org/
http://www.trinitycollege.it/esami/
http://www.cityandguildsenglish.com/
http://pearsonpte.com/

The following is a site containing examples of various types of international certification:  http://www.examenglish.com/  

Some sites are free and are available as downloadable mobile phone apps:

http://www.bbc.co.uk/learningenglish/
http://www.cambridgeenglish.org/learning-english/
http://learnenglish.britishcouncil.org/en/
https://elt.oup.com/learning_resources/
https://www.duolingo.com/
http://www.gcflearnfree.org/topics/everydaylife/
http://www.englishcentral.com/videos
http://www.english-for-students.com/
http://a4esl.org/
https://www.englishclub.com/

Site containing information on MEC, the online course promoted by UNITN, which is used for Blended courses and for self-study on purchase of a login ID and password.

http://www.macmillanenglishcampus.com/

Some newspapers

http://www.theguardian.com/uk
http://www.thetimes.co.uk/
http://www.telegraph.co.uk/
http://www.independent.co.uk/
http://www.dailymail.co.uk/
http://www.irishtimes.com/
https://www.washingtonpost.com/

TV, Radio and podcast

http://www.bbc.com/
http://www.bbcworldwide.com/
http://www.bbc.co.uk/podcasts
http://www.ted.com/
http://edition.cnn.com/
http://news.sky.com/
https://www.youtube.com/watch?v=Ge7c7otG2mk