Robert Tressel's "The Ragged Trousered Philanthropists" is guaranteed to make you cry.

I always find "Watership Down" an emotional read, it's one I go back to again and again, but I only managed to read "The Plague Dogs" once,it was so horrifying.

I re-read Martin Gilbert's book "The Holocaust - The Jewish Tragedy" again recently, it's one that makes you cry at first but the horror goes on and on and becomes worse and worse so that eventually you have no tears left.