I used to display my cards hung on a string, with sparkly plastic clothespins. But a few years back I purchased a card wreath, that I hang over my fireplace. This is a great solution for me, as I have a small house and this allows me to display tons of cards in a very small space. The end result is a really festive and colourful display. By Christmas Eve pretty much all the spaces will be taken up.
Here is last year's display: