Pollack's books are next level stuff for the aspiring historian or devoted student. Moyle's books on Langford and Miske are also excellent. AND of course AJ Liebling's The Sweet Science.
Steve Compton's massive biography of Harry Greb is packed with information and is the most exhaustively researched book on the subject of boxing that I have ever seen. - Chuck Johnston
"50 years at ringside". I have a tattered copy void of a cover that I obtained back in the early 70s. It's still a great read with tons of inside information concerning many past ATG fighters. A must read.
The Road to Nowhere by Tris Dixon is a little bit of a niche choice. A young fan hitch hikes across the US following up on some champions as well as journeymen from the past and takes a look at their lives after boxing. At times it is both heart breaking and heart warming.
John Duncan's 'In the red corner'; is an interesting insight into the Cuban boxing scene in the late 20th Century, with quite few interviews with the players in the sport past and present. As mentioned 'Unforgivable Blackness' is a must have. And Peter Benson's 'Battling Siki' is worth a look.
Three of my favorites: 'Champions Off Guard' by William Inglis 'The Roosevelt That I Know' by Mike Donovan 'Mike Donovan. The Making of a Man' by Marshall Stillman
Facing Ali was perhaps the most enjoyable boxing book I've read. there was such sincerity and warmth for Ali's OPPONENTS as well as him. a very, very good and wholesome thesis.
All three are older books, published in 1932, 1909 and 1918 I believe. But, I also believe the last two might be available as modern reprints now.
I've never enjoyed reading a book more than "The Sweet Science" by A.J. Liebling. Must have read it 3 or 4 times!