I can't show them to you, of course, that would spoil all the fun. I can tell you that the twelve months will show Ned (as seen here, on the cover), Arya, the Kingslayer, Sansa and the Hound, Melisandre, Bran, Daenerys, Jon Snow and Ghost, Robb the Young Wolf, Tyrion at the Battle of the Blackwater, the Mountain v. the Viper, and the Others.
I think you're going like it, kids.
The 2012 calendar will go on sale at the San Diego Comicon in July. John Picacio will be on hand to sign your calendars, and it's possible I may be there as well. Watch my Appearances page for more details on that. For those of you who can't make San Diego, the calendar is available for preorder on Amazon (although those copies won't be signed, obviously), and should be turning up at your favorite local bookstore by August.
Meanwhile, Marc Simonetti is already hard at work on the 2013 calendar.