English quizzes
When I was searching for some useful stuff in the world wide web, I found this BBC homepage:
http://www.bbc.co.uk/worldservice/learningenglish/quizzes/
You can do a lot of quizzes in order to improve your vocabulary skills but also your grammar skills (prepositional phrases,...) but there is also a lot of other stuff that helps you learning English :)
Just try it out!