Candice Millard, River of Doubt (about TR in the Amazon).
David McCullough's Mornings on Horseback, The Wright Brothers, Truman, and The Johnstown Flood are all outstanding (especially if he or Edward Herman narrate).
Bill Bryson, One Summer: 1927 (pop history but very entertaining)
TJ Stiles, The First Tycoon
Morris, The Rise of Theodore Roosevelt
Nelson, The Three-Cornered War