Reddit reviews An Enquiry Concerning Human Understanding: with Hume's Abstract of A Treatise of Human Nature and A Letter from a Gentleman to His Friend in Edinburgh (Hackett Classics)

I think you will learn the most by reading five textbooks, such as A History of Philosophy, volumes 1, 2, 3, 4, and 5; or something like Metaphysics: The Fundamentals, The Fundamentals of Ethics, Theory and Reality: An Introduction to the Philosophy of Science, An Introduction to the Philosophy of Religion, and An Introduction to Political Philosophy.

If what you have in mind is more of a "Great Books" program to get your feet wet with some classic works that are not too difficult, you could do a lot worse than:

• Plato's Euthyphro, Apology, Crito, and Phaedo, often published together under the title The Trial and Death of Socrates. Socrates is so important that we lump together all Greek philosophers before him as "the Presocratics," and this cycle of dialogues is a great window on who he was and what he is famous for.
  
• The Basic Works of Aristotle. "The philosopher of common sense" is not a particularly easy read. Cicero compared his writing style to "a flowing river of gold," but all the works he prepared for publication are gone, and what we have is an unauthorised collection of lecture notes written in a terse, cramped style that admits of multiple interpretations. Even so, one can find in Aristotle a very attractive system of metaphysics and ethics which played a major role in the history of philosophy, and holds up well even today.
  
• René Descartes, Discourse on the Method and Meditations on First Philosophy. Descartes is called the father of modern philosophy, not so much because modern philosophers have widely followed his particular positions (they haven't) but because he set the agenda, in a way, with his introduction of methodological scepticism.
  
• David Hume, An Enquiry Concerning Human Understanding. I think Elizabeth Anscombe had it right in judging Hume a "mere brilliant sophist", in that his arguments are ultimately flawed, but there is great insight to be derived from teasing out why they are wrong.
  
• If I can cheat just a little more, I will lump together three short, important treatises on ethics: Immanuel Kant's Grounding for the Metaphysics of Morals, John Stuart Mill's Utilitarianism, and Anscombe's paper "Modern Moral Philosophy".

I think you would love David Hume.

http://www.amazon.com/Hume-Enquiry-Concerning-Human-Understanding/dp/0872202291/ref=sr_1_1?ie=UTF8&qid=1381844680&sr=8-1&keywords=an+enquiry+concerning+human+understanding

It's a relatively short but very profound read. Basically he concludes that "logic" is a direct result of experience and not of a priori type rationalism. He also concludes that the notion that the future will always resemble the past is just an assumption and unprovable. According to him one cannot prove or disprove the statement "the sun will not rise tomorrow" until it is actually witnessed. The fact that it has risen every single time before does not in any way guarantee that it will rise again (the future resembling the past). The only way one can prove or disprove this statement is to sit there and wait until the next day and see what happens: experience.

His whole idea is that we accept something as "truth" after witnessing a so called effect rise from a so called cause a certain number of times. He calls this "constant conjunction".

http://en.wikipedia.org/wiki/Constant_conjunction

edit: It is commonly stated that Hume has never been refuted. Kant tried, and it is up to you to decide if he was successful. But other than potentially Kant, his work has not been refuted.

> I didn't know that their were multiple versions of metaphysical naturalism, thats very interesting.

For this, I'd recommend looking at Quine, Peirce, Nietzsche, Early Wittgenstein.

> Anything i can read that would expand on these other versions of naturalism?

Well, to put it plainly, secular philosophies - both naturalistic and non-naturalistic - have dominated the discipline of philosophy for more than a century. So your best bet would be to acquire a passing familiarity with philosophy generally (/r/askphilosophy and the Stanford Encyclopedia Of Philosophy are good starting points).

But I'll also throw up a few resources that I prefer for their engaging style:

• How To Make Our Ideas Clear
  
• Enquiry Concerning Human Understanding
  
  Good luck with Nagel!