Pretty simple to grab one. Go to ----> PC News: Giveaway: Get your Anno Online beta key - ComputerAndVideoGames.com About mid way down the page there is a "Registered Users Only" area. Click the link to register that is underlined. After you do, validate your account. Go back to the above link above and fill in your login info your registered username and password. Click get key. You might have to refresh the page as they have a "you were chosen / not chosen" thing. I got my key on the 2nd try. After you get it, go to ----- > Anno Online | Home page and follow the instructions. They have a ton of keys left.
