Hands down for me: Atlas Shrugged. Period.

Catch-22 and Guns, Germs, and Steel

Marcus Aurelius Meditations

Non-fiction..

Rights of Man by Thomas Paine.
Cosmos by Carl Sagan.
War is a Racket by Smedley Butler.

May seem a bit silly but I read Mists of Avalon years ago, and although it is fiction it made me start to realize how competitive religions were in controlling world views. I started to question mine. I grieved when I finished the book.

Dune. Confirmed, not developed.

The God Delusion.
The Age of Reason.
God is not Great .
A Short History of Nearly Everything.

Fight Club

“The Science of Discworld” V1-4 by Sir Terry Pratchett (STP). Covered human history, science, literature, and religion better than any other text I know of. With the possible exception of “Systemantics” by Gall. It explains systems somewhat more succinctly than TSOD, But not by much.

Philip Slater~ "The Pursuit of Loneliness"

At the risk of dating myself a good place for me to start would be 1984, heart of darkness,catch 22. Books like that.

Atlas Shrugged

"A Generation of Vipers" by Philip Wylie, and "Invitation to Philosophy: Issues and Options" by (if I remember correctly (Honer and Hunt).

there have been so many, so VERY many. i don't think one book changed my WHOLE world view, but many books changed many parts of it. a spaniard in the works and in his own write changed my view of writing itself, which is important as i am a writer. stranger in a strange land was seminal. if i listed them all the computer would explode.

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Stiff: The Curious Lives of Human Cadavers
Book by Mary Roach
Made me realize our expensive religious rituals are stupid and inpired me to donate entire body to science when the time comes.

Wow, ill try to narrow it down to just a few.

Ishmael, by Daniel Quinn. If you have not read this, please please do so.

Zen and the Art of Motorcycle Maintenance, by Robert Pirzig

The Demon Haunted World, by Carl Sagan

Tao of Jeet Kune Do, by Bruce Lee

Universe, Earth and Atom, by Alan Nourse

Letter To A Christian Nation by Sam Harris is one of my go-to books when talking to religious people.

The Revolt of The Angels by Anatole France

Wow, this is like asking me about my favorite glass of water. I cannot narrow it down well but I will say that "On the Origin of Species" by Darwin was great AND it sparked a revolution of countless other great books.

I would say the first proper book I read had the most effect. Not because of it's content or story, it was The Kraken Wakes by John Wyndham, which I thoroughly enjoyed, but because it opened up the idea of reading. I never read anything in my own time and only read what I had to at school to get me by. John Wyndham opened up a universe of wonder.

The Grapes of Wrath.

Waaaay too many to enumerate. i know my writing style was more influenced by john lennon's books than by books i consider better written than those; i can't help it. they influenced me. but my worldview, apart from my writing style? hmm. maybe... oh gosh, i could list hundreds. before my eyes went bad i used to read an awful lot. i wish i still could. be that as it may, here are a few... or a few dozen... let's see how far i get before i have to stop myself. in no particular order: cancer ward and pretty much anything else by aleksandr solzhenitsyn, edith hamilton's greek mythology, cry the beloved country by alan paton, the danny kaye around the world story book, stranger in a strange land and pretty much anything else by robert a heinlein, the manchurian candidate, gentleman's agreement, the works of harlan ellison but in particular the glass teat and the other glass teat, all the books i could get my hands on by elie wiesel, elizabeth foreman lewis, chaim potok, stephen becker, charles dickens, thomas hardy, fyodr dostoevsky, primo levi, joanna russ (omg everyone go read all of her nonfiction, not that her fiction isn't wonderful, but her nonfiction is amazing), antoine de saint-exupéry (and pardon me if i have misspelled him), louisa may alcott, robert louis stevenson, mark twain, j d salinger, even albert payson terhune, though thankfully i did not adopt his racism, nevil shute, laurens van der post, desmond morris, robert graves, edward eager, maya angelou, ogden nash, robert lowell, john berryman, i am leaving out a boatload of important influences for sure but these came off the top of my head. oh, lewis carroll and edward lear. nonsense influenced me an awful lot, which is why lennon made such an impression, and that reminds me i should add s j perelman and h h munro to that mix. okay i'll stop but there are so many more....

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The God Delusion
Cosmos
God Is Not Great
The Brothers Karamazov

Atheism the case against god

Probably have to say Anarchist Morality by Peter Kropotkin. I rarely quote it anymore but it lead me down a long path and many of the others that influenced me greatly I may never have read if it wasn't for this book.

Fredy Perlman's Against His-Story - Against Leviathan, a Jaques Ellul's The Technological Society are both in my top 3 as well.