Look at "Five Equations That Changed The World", by Guillen comes to mind. Also, "Longitude" by Sobel.
Harper Collins Dictionary of Mathematics
W.W. Sawyer: What is Calculus About? and Mathematician's Delight
Courant and Robbins: What is Mathematics?
Hogben: Mathematics for the Million
Steinhaus: Mathematical Snapshots
Ivars Peterson: The Mathematical Tourist
Davis and Hersh: The Mathematical Experience
Polya: How to Solve It
Huff: How to Lie With Statistics
McGervey: Probabilities in Everyday Life
Raymond Smullyan: The Lady or the Tiger, Alice in Puzzle-Land
Good Books on Mathematical logic
Logic and structure (Universitext)
D. van Dalen (Hardcover)