In my library pile:
Kepler's Conjecture: How some of the greatest minds in history helped solve one of the oldest math problems in the world, by George G. Szpiro
Painless Algebra, by Lynette Long, Ph.D. (a Barron's guide I'm looking at maybe for Dollygirl in the fall)
The Teaching Gap: Best Ideas from the World's Teachers for Improving Education in the Classroom, by James W. Stigler and James Hiebert
Mathematics: The Science of Patterns, by Keith Devlin. This looks like a very cool book: it's not a how-to, it's more of a why.