EA has been releasing the names of boxers featured in Fight Night Round 4 in drips and drabs but scans from the Official Playstation Magazine have revealed the entire roster. Here's the full list of fifty fighters, via Stick Skills:

• Mike Tyson
• Muhammad Ali
• Ricky Hatton
• Ray Robinson
• Thomas Hearns
• Miguel Cotto
• Shane Mosely
• Jake Lamotta
• Marvin Hagler
• Roy Jones Jr.
• Carlos Monzon
• Jermaine Taylor
• Kelly Pavlik
• Manny Pacquiao
• Pernell Whittaker
• Julio Caesar Chavez
• George Foreman
• Joe Frazier
• Lennox Lewis
• Ray Leonard
• James Toney
• Roberto Duran
• Marco Antonio Barrera
• Amin Asikainen
• Paulie Malignaggi
• Kermit Cinteron
• Eddie Chambers
• Arturo Gatti
• Corey Spinks
• Tommy Morrison
• Sergio Mora
• Fernando Montiel
• Jorge Armando Arce
• Arementa
• Anthony Mundine
• Emanuel Agustus
• Vinny Paz
• Vivian Harris
• Billy Dib
• Diego Corrales
• Erik Morales
• Nate Campbell
• Ronald "Winky" Wright
• Yuriorkis Gamboa
• Nonito Donair
• Arthur Abraham
• Joe Calzaghe
• Roberto Guerrero
• Edwim Valero
• Victor Ortiz

Presumably the roster for the Xbox 360 version is the same, as EA's made no mention of fighters being exclusive to the PS3/360. The scans note that additional boxers may be added as downloadable content after the game's release this summer.