Richard Graham of the University of Nebraska-Lincoln's Love Library has made public a large (183 item) collection of U.S. Government-sponsored comic books and related documents, all downloadable as PDFs. Battle Drugs with Captain America! Stay Healthy with Nutri-Man and Vita Woman (also en Español)! Learn to Duck and Cover! And lots, lots more.
Several people have pointed out this great resource to me, and it's high time I shared it, too. Click here for the main page.