* Descartes' Meditations
* Locke Essay Concerning Human Understanding
* Hobbes Leviathan
* Kant Critique of Pure Reason
* Kant Prolegomena
* Kuhn Structure of Scientific Revolution
* Hegel Phenomenology of Spirit
* Foucault Discipline & Punish
* Sellars Epistemology and the Philosophy of Mind
* Sellars The Scientific Image of Man
* Quine Word & Object
* Davidson On the Very Idea of a Conceptual Scheme
* Nagel What is it like to be a bat?
* Searle Minds, Brains, and Programs
Stanford Encyclopedia of Philosophy [0] has a ton of great summary articles and bibliographies that could definitely keep you busy for a few decades or so. I've never been tremendously into ancient or non-western philosophy, which is a deficiency I aim to correct one day, but there are a ton of great essays there as well.