This is a great, comprehensive site all about Idioms in English. There is a full explanation at the beginning about the differences between idioms, phrasal verbs and proverbs. There is then a full A-Z list of idioms, as well as a list under subject headings. There is a quiz to test your understanding at the end of each section. There are so many idioms on this site, you will be sure to know as many as any native-English speaker!
The Idiom Connection: English Idioms and Quizzes