First, Osprey Men-At-Arms #11: Chasseurs of the Guard, one of their earliest titles. Napoleonic era material, mostly intended for the miniature gamer, to paint the units. Not as informative as later books.
Next, Osprey Campaign #141: Blenheim1704: The Duke of Marlborough’s Masterpiece, the whole series is much more informative. Fairly good read.
Third, Osprey Campaign #145: Battle of the Bulge 1944 (2): Bastogne, a critical battle of WWII. Good book.
And lastly, Osprey Elite #56: Scottish Units in the World Wars, the history of Scots in the wars. A bit better than the first book of this pile, not as much data as the campaign books.