A few favorites of mine:
Dear Mom: A Sniper's View of Vietnam--engaging, and follows the author from boot camp all the way to making some bad choices and ending up in Leavenworth. This book also outed Chuck Mawhinney as being the USMC sniper with the most CONFIRMED kills at 103, and overall, behind Adelbert Waldron with 109 confirmed, the second sniper with the most CONFIRMED kills, dropping Carlos Hathcock to a distant fourth behind Eric R. England.
Blood Trails:The Combat Diary of a Footsoldier in Vietnam--Another great book with the author's life from boot camp to his early retirement from injuries sustained in Vietnam
America's Splendid Little Wars-- A book detailing the strategies and weapons used in the 12 smaller conflicts between Vietnam and the Iraq war. A good read to inform you about what ELSE went on in the 80's and 90's.
The Art of War-- The basis of every Wall Street tycoon's thinking, and some of the essentials to fighting a war.
This Man's Army--Follows an Ivy League student who joined ROTC, and then went to ranger school just before 9/11. One of the first memoirs on Afghanistan published from a Ranger's standpoint. My very favorite book on the war in Afghanistan. Andrew Exum has a knack for writing in a way that draws you in.
I'm also a big fan of Tom Clancy's stuff, especially the Jack Ryan series--my favorite being The Bear and the Dragon, which details a war between China and Russia for Siberia, with help from the US on the Russian side. Lots of logistics and tank warfare, but also a lot of realism and in depth thought by Clancy.