I thought this note from a list-serve I follow might interest some of you:
Library of Congress Civil War Photographs
The online Civil War Photographs provides access to about 7,000 different images made during the American Civil War (1861-1865) and in its immediate aftermath. The images were scanned from the Prints and Photographs Division's collection of original glass plate negatives. In addition, this online offering includes copy negatives made from many of the photographic prints the Division holds. The images were acquired from various sources.