Wrath of the Lich King login screens before, this one is the real deal. It's being reported on by numerous sites, and several people have confirmed its authenticity. The image itself is of a ice fortress. You can see the version, 3.0.1, along with the latest build number and date: July 15, 2008.
Many people will notice that you have to sign in via an email address. This is part of a new system that Blizzard has put into place for the Wrath beta. Essentially, you'll have to create a new "Blizzard Account" to log into the beta. This account is separate from your retail WoW account, however you still have to have a retail WoW account and a beta key to get one. There's not a ton of information out on the new account system they are using for this, but when we have more information on it we'll post it.
For now, enjoy your new login screen!