Historians of the American Civil War suffer from a surfeit of primary and secondary sources. And the problem is only growing worse. Not only do more histories and biographies come out every year, new troves of letters, diaries, and other archival material appear from time to time. Then, previously existing supplies of information–newspaper archives and journal articles provide good examples–are being digitized, making them increasingly available. And instead of making the trip to a local library or depending upon inter-library loans to find books from the nineteenth century, they can be downloaded en masse, without ever leaving the house.
A tiny amount of material is available here through the Resources dropdown menu, including listings of articles in Century magazine, Battles and Leaders, and the volumes of the Military Order of the Loyal Legion of the United States. Another list is of newspapers accessible through the Library of Congress and its Chronicling America project. The memoirs written by Ulysses Grant, William Sherman, and Philip Sheridan (two volumes each) are in plain text files from Project Gutenberg. For other digital versions of these last works, Archive.org is a great site.