That has to be one of my favorite Steinbeck novels. I know it was created out of a sense of political urgency/patriotic duty and not any creative inspiration, but I still feel that it was an amazing piece of literature.
"Johnny Got His Gun" is also one of my favorite war, or to be more specific, antiwar novels.
I know, I know. Dalton Trumbo was a complete pinko and the book was used for nefarious purposes by the radical, peaceniks during The Vietnam War, but I still think it's one of the best novels written on this particular subject.
Along the same lines, what about "All Quiet on the Western Front"? Erich Maria Remarche (?sp?) Although it was a World War I movie, rather than World War II (?)