Apparently thanks to a cross-promo with a Sony Pictures "Family Zone" promo site, U.S. PlayStation Network account holders can make their Sackboys and Sackgirls all Ride-of-the-Valkyries with a free-to-download Norse Mythology costume pack.
Go here, punch the giant "REDEEM" button (be patient) to generate your code, and then redeem that through the PlayStation Network and, poof, Sackboy's ready to romp around in his own Wagnerian opera.
LittleBigPlanet Norse Mythology Code [PlayStation.com via GayGamer.net]