Besides Lisa Randall's excellent book Warped Passages, "The Road to Reality" by Roger Penrose is currently THE book to get in popular physics. Although I have to admit when I got my copy I was in for a surprise. I had seen the high sales rankings and was expecting typical Penrose fair, instead what I found was an ambitious effort that could be akin to a principia for the masses. Penrose basically has the book divided into two parts. In part I, he takes us on a tour of mathematics, devoting a chapter to almost every branch of the field. There are chapters on calculus, complex variables, fourier analysis, group theory, you name it. I find his writing style kind of tough going, his explanations are clear enough but something about it has made me want to take this book in small chunks. This is the only reason I don't give the book 5 stars. Anyway, he doesn't hold back, not only writing a popular book that includes the equations but even assigning little homework problems! Moving on, the second half of the book is devoted to physics. Like the math presentation, Penrose devotes chapters to every topic in physics, so you'll find quantum mechanics, relativity, cosmology, black holes and string theory all here, presented in exquisite detail. In the end I think if you are interested in string theory, cosmology, quantum theory and the like, then you should get the book. Just plan on taking your time to read it.