Asimov, Isaac - The Universe: From Flat Earth to Quasar (Walker, 1971)
This guy has written about a gadzillion books, on everything under the sun, and this is one of my favorites. It's a history book about Astronomy, and it has lots of different types of thinkers represented, including early Frank-types and modern scientific thinkers (some surprisingly ancient). Anyone reading it will develop a good feel for how science is done.
Richard Dawkins, The Selfish Gene (Oxford University Press, 1989) - This is actually a book about evolution and genetics, but it also introduces the concept of memes, a kind of evolutionary theory of ideas. I'm not sure he's right, but it's an interesting theory.
Epistemology - The study of the methods and grounds of knowledge, especially with reference to its limits and validity. (according to the Oxford English Dictionary).
Richard Feynman - The Character of Physical Law (M.I.T. Press 1967) This Nobel-Prize winning physicist has written many readable and interesting books, from college textbooks on physics, to several autobiographical tomes. They all help to give the lay reader a feel for science, and "The Character of Physical Law" is one of my favorites.
Jeans, Sir James - Science and Music (Cambridge University Press, 1937)
This book is a personal favorite, not too technical, about why musical sounds sound the way they do. It was written a while before synthesizers were invented, but anyone who likes to fiddle with electronic music-making will enjoy this one.