Title: Hilbert
Author: Constance Reid
Description: Biography of David Hilbert. Fascinating. Don't have to be D.H. to enjoy it. [the following is added from a duplicate answer - feel free to clean up -- ed.] A beautiful biography of a famous mathematician, showing the passion for knowledge represented by Hilbert and others at Goettingen around 1900. The book has a good description of Hilbert as a person, describes his family and coworkers and (sadly) the decay at the end of Hibert's life as the Nazis took over. I ask some of my undergraduate students to read this so that they can see the excitement of being in our profession. (The book is out of print, I think, but available via half.com or ebay.)
Second recommendation Also, Time-Life, ca. 1965, published one of it's picture books on math, titled of all things Mathematics (as I recall). Check it out if you can find it. Lots of cool pictures. Great for mathematically inclined high school kids.
Note added in edit: The aforementioned book from the Time-Life series also had great pictures of mathematicians. As I recall, there was one of Eilenberg lying on the couch of his Grenwich Village apartment, coat and tie still on. It was captioned with a quote which went, if I recall correctly, "Sometimes I like to think riding on the subway, but mostly I like to think lying down." Absolutely formative in my personal approach to math!
