On Facebook, I saw this and had to share.
My answer: The Bell Jar by Sylvia Plath. I decided not to pick a series because I figured it doesn't count if it's more than one book. I love this book and have read it multiple times since High School. I don't know why it's one of my favorites. It's kind of dark and depressing, but I love it.
My beat up copy
So what's your answer?