BBC
Bbc World Service: Learning English Grammar
The Grammar and Vocabulary area of the BBC World Service site has a section on common grammar problems and a section on idioms and expressions. There are also links to pages that provide English language learning opportunities that...
Other
Clta: Esl Activities Online
This Canadian site offers 40 grammar lessons, as well as lessons in use of idioms and other idiosyncrasies of the English language. There are interactive lessons and quizzes, and reading selections with comprehension questions.