If you've not been following Marcus du Sautoy's The Story of Maths (on BBC 4), you've missed a treat. No, seriously!
Marcus du Sautoy's approach and delivery remind me of a rather less manic Adam Hart-Davis (who is himself a national treasure) and help to make the history of Mathematics not only interesting but informative as well.
And you can still watch the first episode here, and in the process find out more about Pythagoras' Theorem, Euclidean geometry and the Platonic solids. Or, alternatively, you could watch this clip here.
Of course, all of the mathematical advances mentioned above also get a mention in Match Wits with the Kids, along with a clear explanation. You can pick up your copy of the book here.