telemachos

terribly, terribly difficult, but very rewarding

David Hume: An Enquiry concerning Human Understanding and An Enquiry concerning the Principles of Morals (I recommend the Oxford Philosophical Texts editions)

Descartes: Meditations on First Philosophy (The Cambridge University Press edition is very good; it's probably worth buying their Selected Philosophical Writings for a good basic Descartes text)

Plato: Defence of Socrates, Euthyphro, Crito (translated by David Gallop)

Plato: Defence of Socrates, Euthyphro, Crito (translated by David Gallop)

David Hume: An Enquiry concerning Human Understanding and An Enquiry concerning the Principles of Morals (I recommend the Oxford Philosophical Texts editions)

Bernard Williams: Ethics and the Limits of Philosophy

J. L. Mackie: Ethics: Inventing Right and Wrong

Willard Van Orman Quine: From a Logical Point of View

short essays, well-written, very accessible

it's probably worth buying their Selected Philosophical Writings for a good basic Descartes text

J. L. Mackie: The Cement of the Universe: A Study of Causation