mind blown ...what a messed up ending

loved this movie. I had a feeling that the crazy girl was going to do something for her sister, but what she did in the end just blew my mind. I honestly thought she was going to kill herself so that they could harvest her organs for her little sister. But the direction they took at the end made my mind blow up. What a gut wrenching ending. I got the same feeling when I watched The Mist.

Can you guy recommend movies with similar gut wrenching endings like these two? All I can say is WOW. And it was a nicely acted movie too...just nuts.