A History of the Middle Ages
By: Crane Brinton, John Christopher and Robert Wolff
This book is kind of the sequel to Charlemagne and gives a good course overview of the Middle Ages (very euro-centric). Unlike the horribly dire picture presented in A World Lit Only By Fire, this book paints a Middle Ages which is much more progressive than the time before it.
I listen to the audiobook (very long but worthwhile if you are an insane history buff).