Not sure about the most influential books, but I'm a huge fan of Anne Rice/A.N. Roquelare. I love her style of writing. She is a very descriptive author, not only when describing places, but with her characters as well. Through the course of reading her you really get a strong sense that you understand her characters which makes reading her very interesting.
Obviously religious texts have been enormously influential, as well as many scientific publications. These works have had profound impacts on our species and have inspired many beliefs as well as opened up our understanding of our world.
John Ronald Reuel Tolkien' books have influenced so much into media from their release, you can see that in music, books, movies, games and other stuff in this image-related-modern-world.
Not that sure bout movies but A Clockwork Orange, was a real issue then.
