DK Find OutThis fantastic site from Dorling Kindersley covers lots of topics and includes lots of great facts.
Grid ClubThis site has interactive activities covering most subjects.
Primary Homework HelpThis website has lots of information about subjects including History, Geography and Science.
ABCYa (ADVERTS)This is an American website so the spelling activities don't always fit. However there are lots of great games - especially for Maths. You will need to subtract one from your year group to get the grade (so Year 4 is Grade 3).
ABC SplashThis is an Australian website which has lots of great educational activities - especially for Maths.
BBC Bitesize (old site)This archived site still has lots of great English activities including reading, writing, spelling and grammar.