This is the "final" list being reported on EA forums.
Heavyweight
Muhammad Ali
Mike Tyson
Lennox Lewis
Tommy Morrison
George Foreman
Eddie Chambers
James Toney*
Joe Fraizer
Roy Jones Jr.*
Light Heavyweight
Roy Jones Jr.*
Jermaine Taylor*
Joe Calzaghe
James Toney*
Thomas Hearns*
Middleweight
Corey Spinks*
Winky Wright
Sergio Mora
Anthony Mundine
Jake Lamotta
Kelly Pavlik
Amin Asikainen
Marvin Hagler
Carlos Monzon
Arthur Abraham
Roy Jones Jr.*
James Toney*
Jermaine Taylor*
Ray Robinson*
Kermit Cintron*
Thomas Hearns*
Ray Leonard*
Roberto Duran*
Vinny Pazienza*
Welterweight
Ray Robinson*
Corey Spinks*
Arturo Gatti *
Kermit Cintron*
Vivian Harris
Paulie Malignaggi
Pernell Whitaker*
Miguel Cotto
Thomas Hearns*
Victor Ortiz
Emmanuel Augustus
Manny Pacquiao*
Ricky Hatton
Ray Leonard*
Shane Mosley*
Julio Cesar Chavez*
Roberto Duran*
Vinny Pazienza*
Diego Coralles*
Lightweight
Julio Cesar Chavez*
Nate Campbell
Vinny Pazienza*
Roberto Duran*
Edwin Valero
Shane Mosely*
Manny Pacquiao*
Pernell Whitaker*
Arturo Gatti*
Erik Morales*
Marco Antonio Barrera*
Diego Corrales*
Featherweight
Yuriorkis Gamboa
Erik Morales*
Robert Guerrero
Marco Antonio Barrera*
Fernando Montiel
Jorge Arce
Billy Dib
Diego Corrales*
Nonito Donaire
Roberto Duran*
Manny Pacquiao*
* Multiple weight classes
You'll notice there is no Bernard Hopkins, Holyfield and Adamek, these three were some what confirmed as being in the game. EA stated there will be DLC, so the word is there will be fighters you can download at later dates.