Since we're coming up to our exams (most of us, anyway) How about a topic where the best books and online resources are in one place for all to see?
Basically; Just list sites you've used/heard of, and when I'm bothered (once-a-day, maybe) I'll update this first post to keep all the site in it... I'll get the ball rolling.
BBC Bitesize - www.bbc.co.uk/schools/gcsebitesize/
Recommended by HHAT
Just buy some revision books you cheapos.