I got carried away but what follows has been trimmed down a lot. Here are some texts that were interesting and stimulating to me at some point. A fairly eclectic sampling I think.
D. von Hildebrand, Ethics
D. von Hildebrand, The Nature of Love
M. Heidegger, Introduction to Metaphysics
M. Heidegger, Being and Time
D. Hume, Treatise of Human Nature
D. Hume, An Enquiry Concerning Human Understanding
A. Tarski, Introduction to Logic
D. Dennett, Darwin's Dangerous Idea
D. Hofstadter, Godel, Escher, Bach
Kirk, Raven & Schofield, The Presocratic Philosophers
Lucretius, On the Nature of Things
H. Wang, A Logical Journey
J. Searle, The Mystery of Consciousness
I like a good history of philosophy as well. I can vouch for these:
F. Copleston, A History of Philosophy (9 volumes)
W.T. Jones, A History of Western Philosophy (5 volumes)