We came across this fantastic website about English grammar recently: http://www.ucl.ac.uk/internet-grammar/home.htm

It’s been developed by University College London, but appears to be open to everyone (at least it was when we wrote this). If you need to brush up on the active and passive voice, remind yourself when to use capitals or learn more about the difference between the subject and object of a sentence, check it out. 

It is firmly on our Bookmarks list.