Good one on string theory:
The Elegant Universe by Brian Greene
Non-technical, and also covers some of quantum theory and relativity.

As for fiction, much too numerous, though I did love the Ender's Game series[by Orson Scott Card] (would love to read that again, been trying to for a few years now, but I keep spending on other books!). Also:

This Alien Shore (can't remember who by)
The Wiz Biz (unitary of Wizard's Bane & the Wizardry Compiled), the Wizardry Cursed, The Wizardry Consulted, and the Wizardry Quested by Rick Cook
and hundreds (maybe soon thousands(yeah right)) more.