Here are some links that might be of use:

If you want to buy some real past SATS papers then try this: sats-past-papers

If on the other hand you would like to download them for free then this website is a little gem: emaths

One word of warning - these papers are designed to be printed on oversize paper and then trimmed to size, so if you print on a normal printer some diagrams will be the wrong size and any question that requires an accurate measurement will not agree with the given answer. Links below:

For KS2 SATS and for KS3 SATS as well as a Maths Glossary

The Centre for Innovation in Mathematics Teaching has an excellent set of notes and exercises. Some files (like answers!) require a password. I sometimes think that eduction is like a secret society as websites will often have a phrase like "The password is not normally available to individuals who are not part of an educational institution". So much for involving parents in education.

For a range of good (and free) worksheets try NGfL

For some good revision guides try Brookworth publishing. Only buy the guides for the level you need, as there is a lot of repetition between guides. Good value for money if bought direct from them.

Happyanteducation are a new company specialising in primary education. Most helpful support.

Supplier of calculators: Student Calculators

Looking ahead to GCSE, many schools are now using IGSE, as here is no course work involved in this sylabus.

Whilst you are visiting this site take a look for the 'O' level page. Yes, these are still going strong and are popular with the rest of the world it seems.
For the IGCSE maths see: University of Cambridge International Examinations