Is the Pope Catholic? - It's a book about secularism, not religion. I wouldn't pick it up again but I read it at a young age so it's interesting ideas about secularism did get stuck in my head.

The Fountainhead- I liked it because it read like a romance novel, but it wasn't the book itself that stuck in my mind, it was people's reaction to when I talked about the book. It opened my eyes to how controversial some ideas are by people's reaction to it and how a lot of people conform and close their eyes, or act like they are confused about ideas, or that they believe there is a "right" and a "wrong" way to think.

The Midnight Club- Interesting ideas about life, death, reincarnation, and terminal illness. Maybe it was because I was young and I just really liked Pike's YA novels but I felt this one hit deeper and I'll always remember it.