|Marcus Aurelius, bronze fragment, after 170 AD (Louvre Museum)|
From the philosopher Robert Nozick, author of Anarchy, State, and Utopia and The Examined Life (which I am currently enjoying):
There are very few books that set out what a mature person can believe -- someone fully grown up, I mean. Aristotle's Ethics, Marcus Aurelius's Meditations, Montaigne's Essays, and the essays of Samuel Johnson come to mind. Even with these, we do no simply accept everything that is said. The author's voice is never our own, exactly; the author's life is never our own. It would be disconcerting, anyway, to find that another person holds precisely our views, responds with our particular sensibility, and thinks exactly the same things important. Still, we can gain from these books, weighing and pondering ourselves in their light. These books -- and also some less evidently grown-up ones, Thoreau's Walden and Nietzsche's writings, for example -- invite or urge us to think along with them, branching in our own directions. We are not identical with the books we read, but neither would we be the same without them. (The Examined Life, p. 15)
There you have it: a semester's worth of college-level education for less than one hundred dollars. Read the six books listed above and you will not be the same person you were before. (I would personally put Walden at the bottom of the list.)
(By the way, Nozick's The Examined Life is another book that invites us to think along with the author.)
Another note: If you decide to purchase these books, be aware that I tried to link to good editions. There are now a lot of digital publishers cranking out poor versions of noncopyrighted classic works. I highly recommend sticking closer to The Modern Library (can't go wrong with them, in my experience), Penguin, or Signet Classics. Very often, Amazon reviewers will help steer you to the best edition of a classic work.