I've read some of those books cover to cover (Art of War, the Prince) & other's I've glazed over because they were, well, boring & laborious & I don't believe anybody should be recommending them as things to read for enjoyment (Origin of the Species or The Bible, for instance). So here's my list of 8 for things that you'll probably never finish, but extract huge value from anyway.
-Richard Feynman Lectures on Physics - religion
-Donald Knuth Art of Computer Programming - I can fuck around with manuals, other text books, but when I come to read the explanation of a particular concept in TAOCP, I always realise "this is the path of least resistance to understanding X" & then that scares me, because there is so much to know & it's really hard to understand anything well.
-William James The Varieties of Religious Experience For those that deny the possibility of spiritual experience within a naturalistic world view. A lot of atheism that is public today misses empathy with religious experience.
-Martin Gardner's articles
-Douglas Hofstadter - Godel, Escher, Bach & Le Ton Beau De Marot - for those that enjoy spending all day thinking about logic & languages (hello programmers) these two books are romantic pulp - you know you shouldn't be reading them, they are so hopelessly impractical, lofty & philosophical.
-Friedrich Nietzsche - The Gay Science - because it will infuriate people who are adverse to the sort of thinking you see in the humanities and they deserve to be enraged by this book. If you have an ethical system, think you can tell good from bad, right from wrong, read this book. Acid for the normative.
- C.S.Peirce's notebooks - This hasn't been published in its completeness but deserves to be (I just hope saying this here doesn't mean I'll never be able to find a copy of some of his notes again). Another tragic of history that has been looked over in much the same manner as Tesla. Peirce figured out electrical gates could be used to implement boolean logic 50 years before Shannon, axiomatised the natural numbers before Peano, made the distinction of cardinal and ordinal before Cantor & nobody knows who he fucking was because he was a chemist. What else is in his books that we haven't managed to recognise the significance of yet?