Exam Boards

This is the place for syllabuses, exam timetables, and past papers. If you don't know already, your school/college will be able to tell you which board/syllabus you need.
AQA
EDEXCEL
OCR

Revision

I often suggest to my students that they see the material they are learning in as many different ways as possible. The internet is, as you might expect, an excellent tool for this.
I have selected the following websites as being those which I consider the most complete and accurate of the many available. Of course, I'm not making any guarantee that they totally satisfy either of these conditions!

G.C.S.E.

BBC Bitesize
revisionmaths.net
S-Cool

A-Level

revisionmaths.net
S-Cool

Online Graphing Calculators

Students of mathematics at any level will find it beneficial to have access to a calculator that can plot functions (draw graphs). It is not always possible to get hold of one physically, and so here are some free online calculators that I recommend.

Geogebra
Probably the best calculator for GCSE and A-Level students. It does much more than just plot graphs (which it does very well); it can solve equations, do calculus and has an interactive geometry system (great for playing with circle theorems for example.)

Wolfram Alpha
Wolfram call this a 'computational knowledge engine'; roughly speaking this means that it takes data from many different sources and compiles them into statistics, graphs and diagrams. This can cover areas such as maths, physics, chemistry, biology, engineering, economics, politics, sociology...the list goes on. In fact just about any subject which can be approaced analytically is covered.
Wolfram Alpha also functions as a calculator, just about the most powerful calculator you'll ever use. Please try it to find out for yourself just how impressive and diverse the applications of this resouce are. There are buttons for examples and random results above the search bar, these are the best way to find something new and surprising.

General Maths

MacTutor History Of Mathematics
An impressively comprehensive and fascinating guide to the development of mathematics, a subject which has been around for thousands of years. If you have heard of a mathematician and want to know more, this is the place to go.

Mathworld
An extensive online encyclopaedia. Most entries contain way more technical maths than the average person needs, so don't be put off if you don't understand everything!
It's well worth a browse; if you're not looking for anything in particular, try the recreational mathematics section. Yes indeed, maths can be a form of recreation!

The Virtual Math Museum
A large collection of images and interactive 3D applets illustrating diverse areas of mathematics. This can help to visualise and understand a concept you are already familiar with, or you can just browse the pretty pictures!