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Thea Beckman, of course (if you can read Dutch). I feel ashamed that I haven't tried to find and play Du Guesclin.
 
Medieval Russia: 980-1584 by Janet Martin.

An interesting overview, especially given the importance of succession issues to CKII aficionados.

And a bit of context for EU-fans who wonder how Moscow came to be the centre of the Rus'/Russia.
 
I would add Thomas Madden's The New Concise History of the Crusades. "Placing all the major crusades within the medieval social, economic, religious, and intellectual environments that gave birth to the movement and nurtured it for centuries, Madden brings the distant medieval world vividly to life." I agree. :)

I also recommend Triumph: The Power and the Glory of the Catholic Church. While the book covers 2000 years of history, its portion on medieval Europe are particularly interesting to read. "It is a sweeping drama of Roman legions, great crusades, epic battles, toppled empires, heroic saints, and enduring faith. " I thoroughly enjoyed it.