This. Perhaps i'm biased, since i'm supposed to graduate from philosophy department this year, but i do think that reading ancient philosophy (Plato & Aristotle are the most representative example of what was going on there) is the best way to think better -- and get in touch with origins of European culture.

My recommendations, apart from "Sophist" (which is a difficult, very technical dialogue regarding problems with platos theory of ideas) would be "Nicomachean Ethics" (Joe Sachs' translation), "Philebus", "Phaedrus", and of course "The Republic", Platos' magnum opus.