Warfighting is an invaluable resource for anyone interested in the subject. Currently on the USMC Commandants' professional reading list.
Leading Marines (Unabridged)
Chesty: The Story of Lieutenant General Lewis B. Puller, USMC
The Warrior Ethos (Unabridged)
The Marine Corps Way: Using Maneuver Warfare to Lead a Winning Organization
Fields of Fire
Infantry in Battle (Unabridged)