Key Stage 3
BBC Key Stage 3 Science Good general site, with subject content, movies, animations and tests. It's a good starting place for revision for KS3 SATs (FREE)
Doc Brown Key Stage 3 Science Key Stage 3 notes and quizzes. Click on the links for individual sciences to get access to all the notes and quizzes (FREE)
A Level Chemistry
Chemguide - This is a good site for A Level Chemistry subject knowledge (FREE)
FranklyChemistry - Lots of videos about A Level Chemistry (Free)
Corbett Maths - Excellent site for Mathematics with videos, worksheets and practice exam papers (Free)
Key Stage 4
BBC Key Stage 4 Science (AQA) - Unit 1
BBC Key Stage 4 Additional Science (AQA) - Unit 2 For Double Science
BBC Key Stage 4 Further Additional Science (AQA) - Unit 3 For Separate Sciences
This covers all the topics you need to know for AQA Science. There is subject knowledge content, animations, films and tests. Best for pupils who are hoping to achieve up to C/D (FREE).
There are BBC Bitesize pages for Edexcel and OCR Gateway as well. To get to them, simply replace the aqa in the links above with edexcel or ocr_gateway
My GCSE Science - Created by an experienced Science teacher. Subject content for AQA Science. Clear and readily accessible. Good for revision and consolidation. The Core Science Videos are free, the rest you have to pay for.
Doc Brown's GCSE Science Revision - Revision notes for GCSE Science for AQA, Edexcel and OCR. There are also quizzes for GCSE Chemistry and revision notes for A-Level Chemistry (FREE)
Science Revision Videos - by Primrose Kitten. More stuff on her website about Physics and Chemistry