We have been using our Christmas cards to make thank you cards. We did this last year and I cut out bits from the old cards for L to make collages. This year she did all of the cutting, pasting and designing herself.
We've also been making little boxes out of them. For any of you who don't know how to do this I made a little photo tutorial.
First cut your card in half. Then draw an X on both the inside bits.
Fold up each end almost to the center of the X.
Then do the same for the sides. Not quite as close to the center this time.
Cut along the lines created by the folds just until they intersect.
Fold the two side pieces in and then fold the end over top of those pieces. Do this on both sides. You may need a bit of tape or glue to secure them if your ends aren't very long.
Do the same for the other part of the card and you have a cute little box with a lid to store precious Christmas ornaments or treasures in!