A couple more:

They have some great books at the Marine Shop in Quantico, lots of military history but also plenty of works on leadership. The Passion of Command is a big one, I bet you already read that in the rack after lights. My platoon commander recommended a slim book that I picked up but haven't gotten to yet, Battle Leadership by a German WWI veteran, Captain Adolf Von Schell. I also bought a book called From the Horse's Mouth: Selected Thoughts on Small-Unit Leadership. It's a collection of essays and short memoirs of combat, heavy on Marine experiences in Korea and Vietnam, but also including things like a Congo mercenary's tips and "Ten Commandments of the German Parachutist." Highly recommended.