According to Blizzard , Worldwide Invitational '08 and BlizzCon '07 beta code registrations will no longer be accepted for the Wrath of the Lich King beta. Thankfully, the unique pets that go along with this deal can still be obtained.
"Those that still have unused cards will be able to use their code to claim their pet if they have not already done so.
Future beta registrations will be opened after the week of Nov. 13."