One of my degrees was in philosophy, and without being too glib, I'd say not to bother. For me, there were few satisfying reads that deal directly with philosophy, with most of them being a real grind. Maybe Nietzsche, desperate and deluded passionate fellow that he was, is a good read (Thus Spoke Zarathustra), but probably not so worried about clear thinking. Plato can be fun as well (eg. "Trial of Socrates, and "The Cave" excerpt) except when he's banging on about boy love (Symposium).
In particular I found the original works of most of the big hitters to be pretty dreadful (Kant!) and I rarely actually made it through one. If you are truly hell bent on tackling one, I would suggest one of the later critiques or compendiums to start. Durant's "Story of Philosophy" is sort of a standard survey level look at the various schools/studies, and is pretty readable for what it is. Barrett's "Irrational Man" is a pretty good treatment of existentialism. If reading these feels like cheating, just remember it's the ideas that are exciting, not the belaboured dated writing.
I would however enthusiastically point you at the bags of superb "philisophical fiction" that's out there. For instance, as much as I hated trying to read the treatises of Sartre - "Being and Nothingness" (an unreadable pile of merd), Anti-Semite/Jew, The Words" etc., some of my favorite literature was his fiction - Nausea, The Age of Reason trilogy, and his plays. Ditto with Camus (The Myth of Sisyphus vs. The Plague/Stranger/Fall) for some more good existential lit. Toss in the best writer of all, Dostoyevsky to that mix as well.
There's a wealth of quality contemporary "sci-philosphy" books out there as well now that are worth a look. "The Origins of Virtue", "Godel, Escher & Bach", "The Frontiers of Complexity" etc. Good reads the lot of them.
