G. E. Moore, “Proof of an External World” in his Philosophical Papers (New York: Collier Books, 1962), pp. 144-148. Moore’s essay can also be found at multiple sites on the internet.
W. V. Quine, “Epistemology Naturalized” in his Ontological Relativity and Other Essays (New York: Columbia UP, 1969), pp. 69-90.
“Internalism and Externalism,” an article in the Internet Encyclopedia of Philosophy, offers an excellent overview of the strengths and weaknesses of both views and also features a helpful bibliography.