The ones I've read and find good:
- Existentialism is a Humanism - Jean Paul Sartre : Very easy to read and is a very good introduction to existentialism.
- Thus Spoke Zarathustra - Nietzsche
- Siddhartha - Herman Hesse
- Existentialism is a Humanism - Jean Paul Sartre : Very easy to read and is a very good introduction to existentialism.
- Thus Spoke Zarathustra - Nietzsche
- Siddhartha - Herman Hesse
Actually, most books by Hesse have a philosophical element.