The first week it's $100 J!nx gift certificates. In the second week it's World of Warcraft action figures. And for the last week they are handing out an Apple iPod Touch and 2-year WoW subscriptions to five lucky winners.
There are, of course, eligibility requirements, but the basics are that if you have an account in good standing and are 18 or over then you are automatically entered in for a random drawing every day. Check out their official rule page for all the details.
When it comes to contests, nothing beats just showing up to qualify. And who wouldn't want to have their subscription paid for?