Hard to choose. One hand is I would differentiate between fiction and non fiction. On Fiction 1984 by George Orwell. While non fiction is the Fabric of Reality by David Deutsch which has a basic philosophy for understanding reality, specially now with artificial intelligence, genetics, nanotechnology,quantum computing.

I love biography. True stories are my favourites. Open for example is amazing

It would have to be 1984 By George Orwell;
“War is peace.
Freedom is slavery.
Ignorance is strength.”

Illusions. Richard Bach.

Crime and punishment, Dostoevsky

I am torn between both of these titles so am including each of them in my answer. "Godless" by Dan Barker and "The Power of Myth" by Joseph Campbell. "Godless" because my background is very similar to Dan's and I felt a very kindred spirit when reading his words. "The Power of Myth" because it expanded my mind to the wholesale variety of myth and how cultures readily embrace them as a way to explain their world.

British Doorknobs 1812 - 1986

It's a bit predictable I know, but gotta be "a selfish gene" or anything by Richard dawkins for that matter

Manufacturing consent by Noam Chomsky

Godel, Escher, Bach, by Douglas R. Hofstadter. It helped to dispel my remaining mysticism.

The Doors of His Face, The Lamps of His Mouth is a collection of science fiction short stories by American writer Roger Zelazny