Try exploring the following links. Some are useful for particular topics, others for general chemistry and some are useful for revision.
KS3 Links
KS4 Links
KS5 Links
http://www.sumanasinc.com/webcontent/animations/chemistry.html has some useful animations of a variety of processes.
General Science Questions
These sites allow you to either pose your own questions or browse through archives of previously asked ones:
http://www.newton.dep.anl.gov/archive.htm
http://www.wsu.edu/DrUniverse/Contents.html
http://www.physlink.com/Education/AskExperts/Index.cfm
http://www.ftexploring.com/
http://www.guardian.co.uk/notesandqueries/category/0,,-16,00.html
http://rabi.phys.virginia.edu/HTW/
http://whyfiles.org/