The best short introductory book to the ideas of modern physics in print. Why it's better than others: Feynman doesn't skirt around the mathematics as other popular physics writers do. He takes head-on the challenge of explaining complex math to people at an introductory level, and he does so in a way that makes perfect sense.
These six chapters are actually transcribed lectures from Feynman's stint teaching introductory physics to freshman students at CalTech. These are the six easiest to understand of that complete lecture series and include an introduction to physics, the relationship of physics to the other sciences and the fundamental principles behind mechanics (with an introduction to gravitation and planetary motion), energy and a very brief introduction of the principles of quantum mechanics.
Looking forward to 6 Not So Easy Pieces.