Paulo Coelho's books if you're in high school
1984 by George Orwell and Brave New World by Aldous Huxley, and also Handmaid's Tale by Atwood.
And then Umberto Eco, and the love of my life, Salman Rushdie. Also, even if he is not of the same level as the previous two, do check out Max Barry, and underrated author, as well.
The Republic by Plato
Thus Spake Zarathustra by Friedrich Nietzsche
The Analects by Confucius
Tao Te Ching by Lao Tzu
Black Sun: Depression and Melancholia and Julia Kristeva
Hatred and Forgiveness by Julia Kristeva
Changed my life forever.