Amazon pre-orders will get the "Devastator Pack," which reduces damage and fills the "Unlimited Rage Gauge" more quickly. Best Buyers get the "Infinity Pack," offering the ability to recover from overheating more quickly, and spend more time in "Unlimited Rage."
GameStop's bonuses don't alter your performance in-game at all, instead offering you something to look at on breaks from the game. Pre-orders will include a "combination art and comic book" by Penny-Arcade, half devoted to concept art, and half devoted to Penny-Arcade comics about Asura "and how he would deal with everyday situations."
Update: Trailers for the Infinity Pack and Devastator Pack are available after the break.