here or on the official page here.
You must be 18 years of age or older and a legal resident of the United States or Canada (excluding Quebec). You can only enter once. Make sure your email address is up to date, because that's how we'll get hold of you. Official rules here. Keep your eye on WoW Insider as we continue with giveaway contests all day today and tomorrow!
EDIT: Contest closed. Thanks and good luck to all who entered!