I must read more than most...
Right now it's "Bloodlands: Europe between Hitler and Stalin". It's an excellent book, though not for the faint of heart, since it discusses in detail the mass killings, the famines, and deportations that affected millions of people in Eastern Europe and Ukraine in the 1930's and during WW2.
For anyone who has seen the movie about the young Hannibal Lecter and how he came to be the character portrayed in "Silence of the Lambs" and the movies that spun off from it, this book is proof that such things really did happen.