Shiloh, 1862, by Winston Groom.
The Civil War in the West: Victory and Defeat from the Appalachians to the Mississippi, by Earl J. Hess.
I've always found the western theater in the Civil War to be more interesting than the eastern one. Much more maneuver, covered a much larger area. And whereas in the eastern theater the incompetence was almost entirely on the side of the Union (i.e. the "good guys") with such idiots as Irvin McDowell, George McClellan, John Pope and Ambrose Burnside, in the western theater it was largely Confederate, featuring John Pemberton, Braxton Bragg and John Bell Hood.