Requiem for a Dream by Hubert Selby, Jr.
Good lord this book broke my heart. I've seen the movie, which is very sad and horrifying, but actually reading the story just crushed me.
The story of 4 addicts, what they do to feed their addiction, and where their addiction leads them-very, very sad.
I had a little trouble reading it at first-his style of writing is very strange-but once I got past that I had a hard time putting this book down.