For a site with an extensive collection of Excel files for both GCSE and A level – see Mike Hadden’s MathsFiles site.
There are other  resources also, including some for Autograph.

A useful feature to help explore the Excel files is the option to see a screenshot.

These spreadsheets could be usefully used for demonstrations in the classroom and students could then study the examples further themselves.

The A Level files (scroll down the page) include resources for Statistics and Mechanics as well as Pure Mathematics. Files include some for Further Mathematics, for example Matrices.

The Trapezium rule resource shows a very clear diagram and allows the user to choose the number of strips.

The Statistics resources include a Normal trainer with the option to study ‘backwards’ problems and a very clear contingency table calculator.