Everything and More: A Compact History of ∞, By David Foster Wallace. ISBN 978-0-393-32629-1. This a really good book. A bit eccentric in style, but it works because the subject, infinity, is so complex. The story is mainly of Cantor's work in the modern theory of infinity, but it covers stuff from all periods of history, e.g., Zeno and other ancient Greeks to European mathematics of the 1600's and the discovery of Calculus (Leibniz and Newton.)
This book touches on many complex mathematical ideas, but doesn't get too bogged down with proofs, etc.