High Tech High Digital Library - http://hightechhigh.lib.overdrive.com/
Books
I have read some, but not all of these, if you want recommendations.
Flatland: A Romance of Many Dimensions by Edwin A. Abbott
Thinking in Numbers by Daniel Tammet
Moneyball: The Art of Winning an Unfair Game by Michael Lewis
Logicomix: An Epic Search for Truth by Apostolos Doxiadis
A Certain Ambiguity by Gaurav Suri & Hartosh Singh Bal
Innumeracy by John Allen Paulos
The Music of Primes by Marcus du Sautoy
The Book of Numbers by Peter J. Bentley
Born On A Blue Day by Daniel Tammet
Godel, Escher, Bach: An Eternal Golden Braid by Douglas R. Hofstadter
One, Two, Three...Infinity by George Gamow
The Language of Mathematics by Keith Devlin
A Beautiful Mind by Slyvia Nasar
Excursions in Number Theory by Ogilvy and Anderson
Five Equations That Changed the World by Michael Guillen
The Theory That Would Not Die by Sharon Bertsch McGrayne
The Lady Tasting Tea by David Salsburg
Mathematics for the Nonmathematician by Morris Kline
Infinitesimal by Amir Alexander