ForgottenKnight

"The Republic," "The Trial and Death of Socrates," or anything else on Socrates, especially those written by plato, is good as far as ancient greek philosophy is concerned.
Then there's also Aristotle's "The Nicomachean Ethics." That's a good one for ancient greek philosophy as well.
A short piece that you can find in a library and copy (It's not very long) is Epictetus's "The Enchiridon." That's a wonderful philosophy that although may be a bit extreme, has some wonderful ideas. If you read that one, then I'd also get James Bond Stockdale's Courage Under Fire: Testing Epictetus's Doctrines in a Laboratory of Human Behavior.
If you want to go on the more religious side of things, Dostoevsky's "The Grand Inquisitor" is a good piece of russian literature that proposes arguably the best case for Athiesm there is out there, but in many people's view, still isn't a great enough case.
Then there's more modern American Literature, at least in comparison to Ancient Greek Philosophy, that are great philosophical pieces. One such classic is Melville's "Moby Dick or The Whale." It's a great philosophical text if you read it with a book talk group and discuss it in sections of chapters, but not a piece that you would want to read alone.

Edit in: I came across more philospical books in my collection that I thought I should add in.
"Sophocles I" is a good one on grek tragedies.
"The Narrative of the Life of Frederick Douglass, An American Slave" is a good book with a philosophical aspect to it.
Aldous Huxley's "Brave New World" has a philosophical aspect to it. That vision of the future is often compared to the vision illistrated in "1984."

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