John Prados and Ray Stubbe, Valley of Decision.

Neil Sheehan, A Bright Shining Lie. (Books I-III are perhaps all that is necessary.)

Robert Mason, Chickenhawk.

Philip Caputo, A Rumor of War.

Perhaps more tangential to the intended point of the original query, but a fun read nonetheless (the early Vietnam reporters - Halberstam, Sheehan, Arnett et al - through the coup that toppled Diem): William Prochnau, Once Upon a Distant War.

Speaking of Halberstam, I have actually never read either, but do/does The Best and the Brightest and/or The Making of a Quagmire merit inclusion on this list?

And speaking of books not read, here is a book only partially read by me, but which (I think) is thought well of, an assessment I find to be a justified one: Jeffrey Race, War Comes to Long An.

Regards
OC