First and foremost, I would recommend his legendary autobiography, The Personal Memoirs of U.S. Grant (Book|Kindle), which he finished writing just a few days before he died.

•Many Are The Hearts: The Agony and the Triumph of Ulysses S. Grant by Richard Goldhurst (Book)

•Grant’s Final Victory: Ulysses S. Grant’s Heroic Last Year by Charles Bracelen Flood (Book|Kindle)

•Grant by Jean Edward Smith (Book|Kindle)

•Grant and Sherman: The Friendship That Won The Civil War by Charles Bracelen Flood (Book|Kindle)