UPDATE: The deal is now taking place and Club Penguin has sent out an email about it. Thanks Azerty15!
Starting tomorrow and ending the 24th of December, Club Penguin will be running a special limited time membership deal. If you buy one month of a Club Penguin Membership you will get a bonus month for free! It is unknown if it is only for a single month or if it is for all memberships, such as you buy 1 year and get 2 years free. If I find out any more information on this I will update this post.
Thanks goes out to Revgreen, as I saw the post about it on his website.