The New York Times Book of Mathematics

This is perhaps not an obvious choice for Computing teachers, you might think, a book on mathematics. But this one is fascinating because there are sections on cryptography and computing, as well as odd chapters on interesting topics like random numbers and electronics.

The subtitle of the book is More than 100 years of writing by the numbers. In other words, this is a collection of articles taken from the New York Times over the last 100 years. It's readable for non-mathematicians (well, mostly), and gives you a great historical perspective of how computing – and thinking about computing – has developed over that time.