Many of the books noted so far are excellent, and definitely worth your time, but before any of them you need to read Five Years to Freedom, by Colonel James N. Rowe, USA. Colonel Rowe tells the story of his capture by the VC in the early "advisory" days of the US involvement in Vietnam, back when he was a Special Forces Lieutenant. He and his fellow prisoners spent five years being starved, beaten and otherwise tortured and mistreated in a tiger cage before he escaped and was repatriated. His book is a testament to the true meaning of keeping the faith.
The US Army SERE program was started by Colonel Rowe based on his experiences at the hands of his "benevolent" communist captors.
Filipino communists murdered Colonel Rowe in 1989 for embarrassing the Viet Cong in his book. His murderer was recently released from prison.