Ulysses S. Grant : Memoirs and Selected Letters : Personal Memoirs of U.S. Grant / Selected Letters, 1839-1865 (Library of America)
This is probably as good as memoirs get. He is humble. He is self-deprecating. He is forthright. He is willing to defend the decisions he feels need defending. He comes across as very admirable and if I knew nothing else about the man, I would believe that Grant was great. It certainly seems he was well intentioned. I doubt there's a better and less self-serving bio out there from that century, let alone the civil war. Also, Lincoln comes off looking great, as usual.
 - Mary D. McFeely, William S. McFeely, Ulysses S. Grant)