AJ Liebling, "The Sweet Science" - Liebling was the boxing writer for The New Yorker, and probably remains to this day the best boxing writer ever. The annual BWAA award for writing is named after him. These collection of pieces range from the late 1940s or so to the beginning of the television era, which Liebling railed against.
Joan Didion, "On Boxing" - The perfect counterpoint to Liebling's classic is Didion's more contemporary collection of essays on the sport, written from the 1980s through to her work on Mike Tyson in the early 1990s. Not a fan of Liebling herself--she felt he was somewhat condescending in tone toward the fighters--Didion's approach to boxing is that of an ambivalent, intellectual fan who loves the sport but is kind of afraid of the reasons why.
V/A, "At the Fights" - A fascinating collection of great American writers writing about boxing. The highlight for me is HL Mencken's absolutely brilliant account of the Dempsey v Carpentier fight. Others include literary legends like Sherwood Anderson on going to a Joe Louis fight, Jack London's (racist) account of the aftermath of Johnson v Jefferies, James Baldwin's moving portrait of Floyd Patterson, etc., as well as the usual suspects Norman Mailer, Liebling, Didion, and up through contemporaries like Thomas Hauser's excellent work on Don King; even our favorite curmodgeon, Larry Merchant, is included.