I have been mulling over the philosophical works that were of most influence upon me when I was developing into the warped and twisted thing I am now. Add your own in the comments.:
Herbert Marcuse, One Dimensional Man. This book got me interested in philosophy and social issues. I was 16 when I read it.
David Oldroyd, Arch of Knowledge. This book gave me a historical approach to the philosophy of science that has never left me. Although badly typeset, it is rich with information and context of scientific philosophy. I wish it were reissued, properly set.
Antony Flew, An Introduction to Western Philosophy: Ideas and Argument from Plato to Popper. This book grounded me in the traditions of western philosophy in a way nothing else did. Flew attends to the core arguments in their own words. This is a book to buy and reread, and I have gone through several copies giving them away to students and interested lay folk.
Stephen Toulmin, Human Understanding. This was the first evolutionary epistemology I ever read, and to my mind Toulmin got most things pretty well right. It took me thirty years to find a copy of my own.
David Hull, Science as a Process. I did my masters on this book, and David became a mentor. I still think his conceptual inclusive fitness account of science is correct, although I now do not think he entirely got the history of systematics all that right.
In addition to these are the usual canon fodder: Wittgenstein’s Tractatus Logicophilosophicus, Philosophical Investigations, and On Certainty; Locke’s Essay; Hume (anything of Hume, really, but especially the Treatise); and a few deviants, like F. H. Bradley’s Ethical Studies, and Zen and the Art of Motorcycle Maintenance (I read it as a lad of 14. I now disagree with almost everything it in apart from the joy of riding motorcycles).
What philosophical books warped you?