My field of study (what I really like to think and learn about) isn't my field of work, but I like the question so I'll spill some thoughts.<p>I spend a lot of time thinking about philosophical-ish stuff, so here are some books that have had the strongest residual effects (whether that's changing how I think, changing what I think about, changing my values, or simply getting the thought ball rolling faster):<p>Ishmael (Daniel Quinn)<p>1984 (George Orwell)<p>Brave New World (Aldous Huxley)<p>Godel, Escher, Bach (Douglas Hofstadter)<p>The Republic [imp. "the allegory of the cave"] (Plato)<p>The Genealogy of Morals (Friedrich Nietzsche)<p>The Social Construction of Reality (Peter L. Berger, Thomas Luckmann)<p>Tractatus Logico-Philosophicus (L. Wittgenstein)<p>Dissemination [imp. "The Pharmakon"] (Jacques Derrida)<p>The Quest for Reality (Barry Stroud)<p>Languages of Art (Nelson Goodman)<p>The Structure of Scientific Revolutions (Thomas Kuhn)<p>Concepts (Jerry Fodor)<p>The Web of Life (Fritjof Capra)<p>Foucault's Pendulum (Umberto Eco)<p>Naming and Necessity (Saul Kripke)<p>Zen and the Art of Motorcycle Maintenance (Robert Pirsig)<p>There are others, and a lot of essays (by thinkers like Bertrand Russell, Carl Hempel, Hilary Putnam, WVO Quine, Karl Popper, Alfred Tarski, Gottlob Frege, David Chalmers, Daniel Dennett, Michel Foucault, Jean Baudrillard, Mikhail Bakunin, CS Peirce, and David Hume, among many others), but these seem apropos as they most readily came to mind.