For non-fiction, I'd add The Hell of Treblinka, by Vassily Grossman, a Red Army journalist who was one of the first to enter the death camp. One of the hardest things i've read.

"It is the writer's duty to tell the terrible truth, and it is a reader's civic duty to learn this truth. To turn away, to close one's eyes and walk past is to insult the memory of those who have perished."