In Pursuit of the Unknown by Ian Stewart, 2012, ISBN 978-0-465-02973-0. Subtitle: 17 Equations That Changed the World. This book has a label on the back the says Mathematics, but I think it should be labelled Physics, etc. It is really more about the subjects of the equations than the mathematics. Subjects discusses include Pythagora's Theorem, Logarithms, Calculus, Newton's Law of Gravity, Square Root of Minus One, Euler's Formula for Polyhedra, Normal Distribution, Wave Equation, Fourier Transform, Navier-Stokes Equation, Maxwell's Equations, Second Law of Thermodynamics, Relativity, Schrodingers Equation, Information Theory, Chaos Theory and Black-Scholes Equation.
If you are interested in how mathematics is used in the real world, I think this is a good introduction. It is well written, informative and I think entertaining. Sadly there is no list of books for further reading.
 Purchased from Amazon on 2013-3-7 for $20.51.

One Two Three ... Infinity by George Gamow. Originally published in 1947, this copy was printed in 1967 and includes some revisions from about that time. I bought this book new in about 1968. I was in grade school at the time. I remember reading it and being fascinated by the big numbers (especially the descriptions of infinity) and the various descriptions of Relativity and Cosmogony. This particular edition of the book is probably a bit out of date, there is a more current Dover re-print, ISBN 0486256642. Still, I enjoyed re-reading it and would recommend it to anyone interested in learning about science. I was reminded about this book while reading The Pythagorean Theorem by Eli Maor. His book was so good that I bought a copy of his To Infinity and Beyond and in that book was a reference to this book. So I looked around in my boxes of books and found this book and decided to re-read it. Glad I did.

About Time by Paul Davies, 1995, ISBN 0-671-79964-9. The subject of this book is the temporal realm, the dimension of time. The author is a physicist. In technical literature he is listed as P. C. W. Davies. The subtitle is "Einstein's Unfinished Revolution" and much of the book is about general relativity and time dilation. The book starts with a brief history of how people have (and still do) think about time. Everyone experiences time. In some cultures they claim that all times exists together, others only see the Now. In the novel Slaughterhouse-Five by Kurt Vonnegut, the character Billy Pilgrim becomes aware of his disjointed time travels. Most of "About Time" is about time as it relates to modern physics. Good book. The book has 285 pages, a Preface, a Prologue, 14 chapters and an Epilogue. Plus Notes describing sources of quotes, etc., a Biblography and an Index.