These are some of the books that I will be using as references in the Math Academy. Most are written assuming a good grasp of high school math at least through calculus. However, there are portions that are quite appropriate for interested elementary school students.

Godel, Escher, Bach: An Eternal Golden Braid Douglas R. Hofstadter

A Mathematician Reads the Newspaper John Allen Paulos

Innumeracy John Allen Paulos

Introductory Graph Theory Gary Chartrand

Taxicab Geometry Eugene F. Krause

Six Easy Pieces Richard P. Feynman

Six Not-so-easy Pieces Richard P. Feynman

Fermat's Enigma Simon Singh

A Mathematician's Lament Paul Lockhart

Prime Obsession John Derbyshire

The Calculus Wars Jason Socrates Bardi

The Mathematics of Games John D. Beasley

To Infinity and Beyond Eli Maor

Out of the Blue John Naylor

Nonlinear Dynamics and Chaos Steven H. Strogatz

The Fractal Geometry of Nature Benoit Mandelbrot

Euler: The Master of Us All William W. Dunham

Here's Looking at Euclid William W. Dunham

How to Fold It: The Mathematics of Linkages, Origami and Polyhedra Joseph O'Rourke

The Code Book Simon Singh