Shmoop.com's Vietnam Pages
Student-friendly explanations (including answers to questions like "Why should I care?"). Decent set of resources - definitely worth checking out for classroom use, certainly capable of being an on-line resource for student web-quests or projects.
The Vietnam Center and Archive
Extensive collection of resources, including oral histories - most are American, but there are Vietnamese voices there as well. Images and other items are there.
(A digitized version of Dr. Tram's diaries are here - if you can read Vietnamese, she did draw some pictures in the diaries. Students may still appreciate seeing a few of the pages just to get a more visceral relationship with the book.)
The History Place: Vietnam
Essentially a very detailed timeline and about 20 pictures. Each page of the timeline has an "Easy Print" version for printing and using in the classroom.
American Experience: Vietnam
A PBS site with all the trimmings, including a Teacher's Guide (worth checking out), and links to on-line videos for different events. The Primary Sources page only has 6 or 7, but they're important ones from the government explaining the official rationale for the war (including Johnson's Guilf of Tonkin speech).
A number of myths refuted, including the "Average soldider was 19." Each stat is sourced. The list of sources tends to lean to the right, but I would still trust the facts presented - interpretations may differ (like the "Fact" that America didn't lose, South Vietnam did...)
Vietnam War Documents
A ridiculously extensive list of documents pertaining to the war. Pretty exclusively government-level official resources, however. The resources listed are mostly links to other sites, so some links are no longer active.
Vietnam War Resources
Links links and more links. You couldn't browse every link on this site if you took all summer. Perfect for on-line research (links are categorized and described). Good for HS level, GREAT for AP level students.
Dr. Dung Thuy Tram (Last Night I Dreamed of Peace)
Official Website for the book. Of special interest is the discussion guide and the photos.
Privately run website devoted to all things Vietnam War related. A few short biographies, hundreds of images (not easily downloaded for separate use - will need to use a screen capture tool). A detailed timeline and other resources (of special interest are the items in the "Gear" tab including the Manuals).
Vietnam War Photos
Significant collection of photos, many you've never seen in other places. The "Hippies" section is of interest due to its depiction of soldiers expressing anti-war sentiments.
Grunt Magazine Archive
PDFs of every issue of Grunt magazine, 1968-1971. Use this site with caution. The resources are very good, especially in getting a soldier's eye view of the war, but some of the humor and imagery is adult in nature. If you want to convey what life was like for the average soldier, it would be hard to get better than this, but turning students loose on this site would be ill-advised - use only specific pages you've vetted.
The Lighter Side of Vietnam
Some digitized pages from a book of Vietnam humor, much of it dark. Would help students understand what life was like for soldiers.