You can make christmas shadow boxes out of small kid sized shoes boxes. For example, say you had santa in a sleigh. Paint the entire inside of the carboard box dark midnight blue. Paint snow drops coming down or stars. place the box on it's side. Cut our figures leaving a "tab" at the bottom, fold the tab over to the side. You will glue the figure cutout into the bottom of the box by this tab. (or hang it from the top by a string) You can make rooftops to go in the bottom of the box to look like santa is flying through the air. You can decorate the top edge with paper 'icicles' hanging down. Docorate the outside of the box. it is kinda like the easter peep eggs with the viewing hole, except the viewing hole is big! I suppose you could take a round bleach jug or oatmeal box, but the bottom 4 inches off, and have a similar 'shell' only in circular instead of rectangle.
Cut small circles or squares of old fashioned looking cards and glue silver or gold pipe cleaners around the edges to make old time looking ornaments.
Decoupage them onto a storage box, pencil holder(a cutdown oatmeal box) or plate. Richards crafts has lots of paper mache type boxes in every size. use modgepodge to decoupage.
Very large cards can be cut into stocking shapes (front and back) hole punched around the edges, and "stiched" together with yarn. Kids would have fun with this. You can cut all your cards into same size squares and stich them together this way to make a big paper quilt wall hanging. Or stich together boxes for gift giving.
Glue tiny circular figures onto bottons or pendants and modge podge it.
Cut out the figures very well, and have them laminated. then punch a hole in the top and string them onto shoelaces or neclace cords with jingle bells.
laminated figures can have "stands" glued to the back and can be set up to make a little Christmas town areas. I like to turn little cardboard food boxes into vilages either by using construction paper over the tops of them or covering them with real frosting and candy like I would gingerbread.I place them on a big peice of cardboard covered in foil and glue them down.I cut a door in them and swing it open, windows, etc. Use the little gingerbread men cookies by mothers brand as the people, and I use marshmallow trees in the landscape. You can use card cutout figures in this somehow!
Amazon might have craft books about "recycling greeting cards" or look for more ideas on the net under that topic.