I read:

H. Poincare. Value of science

F. Klein. Development of Mathematics in the 19th Century

J.E. Littlewood. A Mathematicians Miscellany

G.H. Hardy. A Mathematicianâ€™s Apology

R. Courant, H.Robbins. What Is Mathematics?

V.I. Arnold. Mathematical Understanding of Nature: Essays on Amazing Physical Phenomena and Their Understanding by Mathematicians.

What else? The author must be an influent mathematician and the book must not be "just another popular math book".