I received a couple of gift certificates for a bookstore -- really, that's the best possible gift for me: not only is it books, but it's books I get to pick -- and I've already managed to spend most of it. Here are the titles I've bought:
Works of Aristotle, volume 2. This is part of an old series by Encyclopedia Britannica entitled Great Books of the Western World, with two volumes devoted to Aristotle. This second volume has the Nicomachean Ethics, Politics, the Athenian Constitution, Rhetoric, On Poetics, and the biological treatises (the History of Animals, On the Parts of Animals, On the Motion of Animals, On the Gait of Animals, and On the Generation of Animals). Yes, it's all available online, but I want to have them on my shelf as well. That way, when society collapses, I'll still have something to read.
Discourse on Metaphysics and Monadology by Leibniz. Two very short works. I didn't realize how short. All I've read of either one is parts of the Monadology since I reference it in my dissertation. These are also available online (the Discourse here, the Monadology here), as is nearly everything else I bought.
Principles of Human Knowledge & Three Dialogues by Berkeley. Never read, only read about. You can read the Principles here and the Dialogues here.
Dialogue Concerning Natural Religion by Hume. I've read this before but it's been a while. A couple of posts ago, I mentioned Dennett's claim that Dawkins's absurd argument against the existence of God is "as unanswerable" as when Hume presented it in the Dialogue. I don't think it's really the same argument, but I need to re-read it.
An Inquiry Concerning Human Understanding by Hume. I've always seen it spelled "Enquiry" rather than "Inquiry" -- like here -- but that's what's on the cover of the copy I bought.
The Birth of Tragedy by Nietzsche. You can read it online here. This is the one book of Nietzsche's that I've never read at all. Well this and The Case of Wagner.
Twilight of the Idols & the Antichrist by Nietzsche. I've only read sections of both. You can read Twilight here and Antichrist here. I mentioned before that Twilight of the Idols has the greatest subtitle in history.
Thus Spoke Zarathustra by Nietzsche. I've read many sections of this, but have never sat down and read the whole thing cover to cover. Online here.
Philosophy of Biological Science by David Hull. Hull is one of the most important philosophers of biology around (although he passed away a few years ago). This is the most recent philosophy book I bought, and it's about 40 years old.
The Abolition of Man by C. S. Lewis. I gave my copy to my promoter after I defended my dissertation. Some may say that this shouldn't qualify as philosophy, since it's written by an outspoken Christian apologist. Obviously they haven't read it. Even though it's not in the public domain, it's available online here.
I also bought a book I used to have, but I loaned out and never got back: Letters from a Skeptic by Gregory Boyd and Edward Boyd. It's an interesting series of letters wherein Gregory Boyd tries to convert his father to Christianity, and is ultimately successful. Not that I agree with all of his explanations, in particular his defense of openness theology in order to explain the problem of evil. Like I wrote before, the oddity of openness theodicy is that in their attempt to solve the problem of evil, they produce the very worst theodicy possible. Despite this, Gregory Boyd's letters are very insightful and the book is well worth the read.
Also some science-fiction:
The Plot to Save Socrates by Paul Levinson.
Singularity Sky by Charles Stross.
The Ophiuchi Hotline by John Varley.