O'Brien's home page has a bibliography and a ton of good links. Note that it's not run by O'Brien himself, but by someone who claims to have access to him. (Also note the unintentionally hilarious editorial comments from the webmaster that are strewn throughout the page.)
This is a comprehensive glossary of Vietnam War jargon and terminology. If you were wondering what a Bouncing Betty, M-60, or Freedom Bird was, this is your site.
Time magazine published a photo essay that shows what American soldiers in Iraq "carry." It's fascinating stuff, and references O'Brien.
A super useful index to the book, assuming you have the correct edition.
PBS presents a site dedicated to the military history of the Vietnam War. It includes detailed descriptions of weaponry and strategies used on the battlefield.
A made-for-TV movie adaptation of "Sweetheart of the Song Tra Bong," starring Skeet Ulrich and Jack Bauer. (Whoops, sorry. Kiefer Sutherland.)
Released in 1979, this classic movie about the Vietnam War is obviously not an adaptation of O'Brien's work, but it's worth watching anyway to really enrich your understanding of O'Brien's world.
An interview O'Brien gave to The New York Times right after the publication of The Things They Carried, in which he discusses his storytelling style.
Time's original review of the novel in 1990.
The original review of the novel by The New York Times.
Tim O'Brien reads from "The Lives of the Dead." The man apparently never takes off his hat. We think he might be bald.
Dylan Baker readers the title story aloud. From Public Radio International's Selected Shorts podcast.
NPR's Terry Gross interviews Tim O'Brien on Fresh Air. (May 31, 2010)
NPR's Talk of the Nation discusses The Things They Carried 20 years after the book was published. (March 24, 2010)
Here's a picture of Tim back when he was a soldier in Vietnam.
Here's another picture of O'Brien while in Vietnam.
And here's a picture of the man now. He's always wearing a baseball hat. We swear.
Here's a map of Quang Ngai, the province that O'Brien marched through as a soldier.
And, by the way, that's a communist flag they're holding up (presumably because they found it, not because they were flying it).