I'll give you two: Brave New World by Aldous Huxley and The Handmaid's Tale by Margaret Atwood. After reading each one, I had to sit in quiet contemplation in order to fully absorb everything I had just read. Brave New World challenged my understanding and science and culture as well as teaching me to view the function of religion in society. The Handmaid's Tale introduced to me Second Wave Feminism and was the first time I'd ever seen sex distorted and used as a means of control (hey, what can I say, I was very young the first time I read it).