Defenders of the Faith: Charles V, Suleyman the Magnificent, and the Battle for Europe 1520-1536 by James Reston, Jr. (nonfiction)

With an amazing cast of characters like Henry VIII, Francis I, Charles V, Suleyman, Ibrahim Pasha, Barbarossa, and Martin Luther, you can't go wrong.  This is good stuff, never a boring recitation of facts.  The book has a reach that isn't so broad that it dilutes itself.