Matterhorn by Karl Mallantes, a brutal description of Viet Nam from the fighting man. Egotistic senior officers, hard NCOs and racial tensions all make a good read.
I'd like to second the vote for this book, although its fiction its a great read.
Also just finished 'Seven Troop' by Andy MacNab. His fiction is good, but this true story of his early days in the SAS is fascinating. However, it is the last few chapters, which recount the lives of many ex-Seven Troopers that make it moving and memorable. It also serves as a warning to the future.