This site has games and other resources as well as exam tip and strategies.
This site links to old spec but still very useful and registration is free.
S-cool - Choose an activity, revise it, test it and remember it! S-cool includes overviews, exam style questions, multiple choice questions and revision summaries on a range of GCSE science topics.
GCSE Bitesize - A classic revision aid with subject overviews, interactive activities and questions on a variety of topics from different syllabi.
Khan Academy - With over 3,100 videos on everything from arithmetic to physics, your GCSE students should be able to find videos on the topics they need.
YouTube - How about curating your own revision video playlist for your students? You can tailor the videos to topics that your pupils need help with. Check out the Planet Science YouTube playlists for inspiration.
TES Games for Grades - A collection of the most popular revision games and activities on TES Science.