Official Records (The War of the Rebellion) (link to all, via Cornell University)

The War of the Rebellion: a Compilation of the Official Records of the Union and Confederate Armies: Full Text Copies of All 128 Volumes, Presented by Cornell University
http://ebooks.library.cornell.edu/m/moawar/waro.html

Author: United States. War Dept.
Title: The War of the Rebellion: a Compilation of the Official Records of the Union and Confederate Armies
Other Title: Official records of the Union and Confederate armies
Publisher: Government Printing Office
Place of Publication: Washington
MoA Volumes: Series I, 1-53; Series II, 1-8; Series III, 1-5; Series IV, 1-4 (1880 - 1901)

I have to use Official Records all the time, and I love finding the full books online, with the original images. Unfortunately, this site may limit access, or prevent links. I find that sometimes the link won't work (internal server error). It could be because I've called on the source too many times, or it could be that they don't like deep links to their site. Try it. If it works, it's worth a mint!