David Prendergast - a lawyer, a Vietnam Veteran and an advocate for Vietnam Veterans for over thirty years - recently launched a web site which contains the entire document archive for the U.S. Marine Corps for all units deployed to Vietnam from 1960-1975. It's a subscription based site and you have to pay a monthly fee for access, but the site has an index of links that are useful and the preview is cool (Battle of Chu Lai info).
This archive contains the monthly command chronologies, after action reports, operational reports, and much more. David uses this material to validate veteran stressors and to document events for narratives submitted with V.A. disability applications.
This information is an amazing compilation of the heritage and valor of Marine Vietnam Veterans.
Thanks to Seamus and Gunny Jim Gregory for the link.