World of Warcraft:Cataclysm is now open for closed beta opt-ins. As some of you may know the alpha was only available to friends and families of Blizzard employees. The only requirements needed to participate in the beta is to have a Battle.net account that has a World of Warcraft account tied to it and details about your system specifications. After doing that make sure you check the box for World of Warcraft beta.
More info can be found here.