BBC GCSE Bitesize Revision
Choose your subject and start revising!
https://www.bbc.com/bitesize/levels/z98jmp3
Revision World
Great for GCSE and A level revision. The site is growing all the time and has examples of past papers and free online Letts guides too.
http://www.revisionworld.co.uk/
Sparknotes
Very good educational web site. Information on a wide range of subjects, notes on set books. Search facility.
http://www.sparknotes.com