All Hell Let Loose: The World at War 1939-1945. Paperback. By Max Hastings
Prince on Amazon from 1p plus P&P.
I've read a few books by Hastings and although I stand by a lot of his opinions I'm not a huge fan of his but this book is definitely worth having. It's an overview of the conflict by zone/front and it's certainly packed with useful facts. At the price it's being offered it's not going to hurt your pocket either.
It's got to be ten out of ten for this one and it's rare I would say that.