Sassy Sites has a Christmas card holder that I love:
She got the idea to use shutters from A Diamond in the Stuff:
And I saw this one at Pretty Handy Girl and she uses clothes pins to secure hers, which could be decorated with some red and white stripes to make them even more festive:
And the best part is that if you decide to make them now, you don't have to put them away after Christmas! You can just use the shutters as a regular message board like How Does She:
I have always been a fan of shutters, so I have to say that this is one of my favorite ideas for displaying Christmas cards.