Dictionaries

Monolingual Dictionary

Oxford Advanced Learner’s Dictionary (OALD)
www.oxfordadvancedlearnersdictionary.com
This is the best monolingual learner’s dictionary of English. A learner’s dictionary gives special help with the things language learners need—irregular forms, dependent prepositions, formal/informal language, particular grammar, etc.

Bilingual Dictionaries

Use a monolingual dictionary to understand how to use new vocabulary (for example when you want to write). Use a bilingual dictionary when you need to quickly check the meaning of a specific term.

IL RAGAZZINI 2012, Dizionario Inglese-Italiano, Italian-English, Zanichelli (print)

Corriera della Sera
http://dizionari.corriere.it/dizionario_inglese/
Collins Reverso
http://dictionary.reverso.net/italian-english/
Word Reference
http://www.wordreference.com/

Oxford Paravia
http://oxfordparavia.it/

Other dictionaries
http://dictionary.cambridge.org/
http://dictionary.cambridge.org/dictionary/british/italian_1
http://www.stars21.com/dictionary/English-Italian_dictionary.html
British National Corpus
http://www.natcorp.ox.ac.uk/
A corpus is the raw material of dictionaries. Look up any word or expression to see examples of how it combines with other words in native-speaker English.
Grammar Exercise Books
Essential Grammar in Use – Raymond Murphy, Cambridge University Press
English Grammar in Use – Raymond Murphy, Cambridge University Press

Advanced Grammar in Use – Martin Hewings, Cambridge University Press

Grammar Reference Book
Practical English Usage – Michael Swan, Oxford University Press

Sites where you can study English

Here is a site where you can check and practice grammar structures:
http://www.ego4u.com/en/cram-up/grammar
(from here you can also access reading and other resources)
There is also:
http://vivquarry.com/wkshts/
e.g. http://vivquarry.com/wkshts/linkwd2.html
and
http://esl.about.com/od/writingadvanced/a/wc_addition.htm
but the best sites are:

Exam English ✓Free Practice Tests for learners of English

http://examenglish.com/cambridge_esol.php
for lots of free practice material at different levels (about this more later)
and BBC Learning English
http://www.bbc.co.uk/learningenglish new address
and http://www.bbc.co.uk/worldservice/learningenglish/general/ old address (but still active)
you should explore the site. For example:

http://www.bbc.co.uk/learningenglish/english/features/6-minute-english

http://www.bbc.co.uk/worldservice/learningenglish/general/sixminute/

is for listening practice and dictation

http://www.bbc.co.uk/worldservice/learningenglish/language/

is for grammar, vocabulary and pronunciation

Other sites where you can practice English

iTunes U (via iTunes , which you must install)
http://www.apple.com/it/education/itunes-u/
video and audio podcasts of university lectures and courses. See how your subject is taught in English.
TED (Technology, Entertainment, Design)
http://www.ted.com/
Fantastic presentations from some of the most innovative people in the world. Watching presentations is a really good way to practice comprehension.

The Purdue Online Writing Lab

http://owl.english.purdue.edu/

Online distance courses (MOOCs – Massive open online course)

http://en.wikipedia.org/wiki/Massive_open_online_course
http://www.bdpa-detroit.org/portal/index.php?Itemid=20&catid=29:education&id=57:moocs-top-10-sites-for-free-education-with-elite-universities&option=com_content&view=article
http://www.moocs.co/
http://www.mooc-list.com/

TV Channels

The aim here is to listen and improve your comprehension, stay up to date (so you should also follow the telegiornale in Italian) and absorb some of the language.

BBC

http://www.bbc.co.uk/

France 24 in English

http://www.france24.com/en/

Aljazeera in English

http://www.aljazeera.com/

You can also get a wide range of live TV channels on:

http://www.filmon.com

and shows on:

http://allnewepisodes.com/tvshows/