the next World of Warcraft expansion has begun. Invites are going out now to players around the world who've signed up on Blizzard's Battle.net service, although there's no indication yet of just how many invites are out or how big the beta will be. If past tests are any indication, Blizzard will likely start it small and expand over time -- that's how the StarCraft 2 beta played out.
This also means that information about the new expansion will start appearing online -- rumor has it that there is no NDA for the closed beta experience, so players who see the new content will be able to tell us all about it. Cataclysm will completely revamp the old World of Warcraft world, in addition to adding five more levels of content at endgame. The Wrath of the Lich King beta also began in early July, and showed up in stores in November a few years ago, so it's reasonable to assume the same timeline for Cataclysm.
In the meantime, if you want to play, make sure your Battle.net account is set to opt-in and keep an eye out for a beta notice in your inbox. Good luck!