I teach high school phys and chem and like to use
thinkquest there are tons of parts to it, so you can sue it for a huge number of topics.
I also like the following site out of the UK:
gcsebitesize . It is based on their high school curriculum and has both info parts (called revision sections) and practice tests. Once you go to this site, chose science link near the top then you will get a screen which asks you which exam board you're in, for us here in the US it doesn't matter which one you choose, the core science links are a bit more basic but the additional science has more for some topics.