Here are a few books relating to tactics and training that have been worth the read:
Brian Enos, Practical Shooting
Mark Walter & Kathy Jackson, Lessons from Armed America
Col. Grossman, On Combat and also On Killing
Jim Cirrillo, Tales of the Stakeout Squad and also Guns, Bullets, and Gunfights.
Massad Ayoob, The Ayoob Files; The Book