BBC Maths
Key Stage 3 and GCSE maths support
http://www.bbc.co.uk/schools/16
IXL
Check out this great site covering Maths skills from reception to year 12.
http://uk.ixl.com/
Maths is Fun
Suddenly maths doesn't look quite so hard!
http://mathsisfun.com
Murderous Maths
Based on the popular books. You'll find 100s of pages of tricks and games as well as lots of help with your maths!
http://www.murderousmaths.co.uk/