One of the first person accounts I have of the Civil War is that of Samuel W. Crawford, the surgeon at Fort Sumter at the time of the 1861 seige. I read it while I was documenting Fort Sumter for the Historic American Buildings Survey in 1991. You can view the drawings through the link provided. It is a fascinating account as he appeared to be striving for the type of accuracy Blight said many veterans were at the time. Crawford wrote the book in 1887.
Crawford was also at Antietam, Gettysburg and a number of other battles during the Civil War. He also was involved in efforts to preserve the Gettysburg Battlefied after the war.