The Oregon Military Museum is located at 15300 SE Minuteman Way in Clackamas. The museum's mission is "to inspire and educate visitors about Oregon's military heritage and legacy." You can find information about the museum and its exhibits on their website.
The National Archives is the nation's record keeper. They archive and store documents and materials created in the course of business conducted by the United States Federal government. In their Veterans' service records archive you can request military service records, research using military records, replace lost medals and awards, browse WWII photographs, and more!
The Civil War Soldiers and Sailors System (CWSS) is a database full of information about the men who served on both sides during the civil war. The CWSS is a collaborative effort by the National Park Service and several other partners with one goal in mind: increase understanding of the civil war era by making information about it widely accessible.
The National WWII museum's website offers people across the world the opportunity to browse a sample of the full collection of thousands of oral histories and photographs. Images are available for purchase if desired.
Texas Tech University has created a virtual Vietnam archive which consists of over 7 million pages of scanned materials pertaining to the Vietnam war. You can use the above link to search the archives or browse materials in their digitized collections.