Nausea by Sartre
Ethics by Spinoza
The art of war by Sun Tzu
Meditations by Marcus Aurelius
The Prince by Machiavelli
The Divine Comedy by Dante
Biographies of Dante, Michelangelo, the Medici, Titian and Filippo Lippi
Candid by Voltaire
We by Zamyatin
Aristotle (poetics, physics, etc)
Albert Camus (myth of sysiphus, the stranger, the plague)
Max Weber
Illiad by Homer and Odyssey
Das Kapital by Marx
On Liberty by Stuart Mill
An essay concrning human undertanding by David Hume (and Locke)
The world as will and representation by Schopenhauer
Tao te ching by Lao tzu
Leviathan by Thomas Hobbes
The Social Contract by Rousseau
Fear and Trembling by Kierkegaard
The republic by Plato
Nicomachean ethics by Aristotle
1984 + the animal farm
Solaris
The Metamorphosis by Kafka
The master and margarita
Siddhartha
Fahrenheit 451
The Brave new world
The 5 books from dostoevsky
Nietzsche
Essais by Montaigne
The brothers Strugatsky, douglas rushkoff, epictetus, thomas acquinas, Confucius, descartes, freud, heidegger, darwin, hawking, einstein, francis bacon, piaget, wittgenstein,
These are at the top of my head, also read you should popular authors in your country.