First was Osprey Men-at-Arms #45: Napoleon's Polish Troops. It gave a good history as to what was happening to Poland during that period, and why so many Poles were willing to fight under Napoleon's command.
Second was Osprey Duel #31: British Dreadnaught Vs. German Dreadnaught: Jutland 1916. Much of this was covered in the Campaign book about Jutland, though this mostly dealt with the ships, and only to a lesser extent with the tactical situation. Honestly, I liked the Campaign book better; just me, I suppose.