Atlas Of The Medieval World by Rosamond McKitterick (2004, Hardcover)

You can tell this is written by an academic because of it's well defined facts but, it's not written just FOR academics. The lay out and flow makes for an entertaining, while very informative read. There is a map for nearly every question you may have however, I was a little vexed that more then a few references in the text was not on the corresponding maps.
All in all I would highly recommend this book to even those with a passing interest in the world the way it was because I feel it could give a lot of folks an insight in to why some things are the way they are today.