I also enjoyed Jake Lamotta and Rocky Graziano's books, because they both have very incredible (and similar) stories, and both are incredibly honest (particularily Lamotta, who does not try to hide the fact that he was a sick sick F##ker.)

"A Flame of Pure Fire: Jack Dempsey and the Roaring 20's" is a great one too, because not only does it go over everything you ever wanted to know about Jack, but it paints a historical context and you realize just how much he meant not only to the sport but to America at the time (just like Louis after him).