Hierarchical order would be unfair...
1. Henry Miller - Tropic of Cancer / Tropic of Capricorn
2. Albert Camus - The Stranger
3. Herman Hesse - Steppenwolf
4. Ernest Hemingway - For whom the bells toll
5. Julio Cortazar - Rayuela
6. Jasper Ridley - Mussolini
7. Juan Rulfo - Pedro Paramo
8. Paco Ignacio Taibo II - Ernesto Guevara also known as 'Che'
9. Jean Paul Sartre - Nausea
10. Jack Kerouac - On the road
And I forget a lot, damn... no SciFi though, I loath it
Here are some of my favorite Sci-Fi books:
Poul Anderson, Brainwave. Also Boat of a million years. Talk about prolific!
Spider Robinson, Callahan's crosstime saloon and Callahan's Lady.
He is also prolific, lots of Callahan stories.
Mary Doria Russell, The Sparrow and sequel, God's children.
She knows more about humanity than anyone!
Olaf Stapleton, the starmaker, oldie but definitely goodie!
Orson Scott Card, the Ender's game series. Also the Memory of Earth series., the Alvin series (fantasy)
I'll leave it at that for now for Sci Fi.
The Other America, Harrington
Daniel Quinn, Ishmael
Name of the Rose, Umberto Eco