Below are various links to resources and past exam papers, that you can view and download.  

More subjects to be added.

History

https://www.youtube.com/user/revisegcsehistory

http://www.bbc.co.uk/schools/gcsebitesize/history/

http://www.hodderplus.co.uk/myrevisionnotes/gcse-history/ocr-a/index.asp This link includes OCR past papers which you can download and practise exam style questions using any of the past papers.

Science

http://www.aqa.org.uk/subjects/science/gcse/science-a-4405/past-papers-and-mark-schemes  (core Science)

http://www.aqa.org.uk/subjects/science/gcse/additional-science-4408/past-papers-and-mark-schemes  (additional Science)

http://www.aqa.org.uk/subjects/science/gcse/further-additional-science-4410/past-papers-and-mark-schemes  (further additional science)