U.S. Civil War and Reconstruction: a Research Guide

Virginia Center for Digital History, University of Virginia.
“The Valley of the Shadow Project takes two communities, one Northern and one Southern, through the experience of the American Civil War. The project is a hypermedia archive of thousands of sources for the period before, during, and after the Civil War for Augusta County, Virginia, and Franklin County, Pennsylvania. Those sources include newspapers, letters, diaries, photographs, maps, church records, population census, agricultural census, and military records.” – description from Web Site.

U.S. Library of Congress. (one of the American Memory collections.)
A Century of Lawmaking provides access to digital images of pages from the Congressional Globe (now called the Congressional Record). Debates and statements made on the floor of the U.S. Congress about the “rebellion” are easily located from the "Search All Titles" screen

The Avalon Project at Yale Law School.
Includes Declarations of Secession from some of the Confederate states, and messages and papers of the Confederate government

United States Senate.
Links to documents, debates, and speeches in the U.S. Senate on war-related issues in the years leading up to and during the Civil War.