I read the following from Real Simple magazine.
St. Jude's Ranch for Children (http://www.stjudesranch.org/help_card.php), a non profit home for abused and neglected youths, runs a holiday-card reuse program in which the kids cut off the front covers, glue them onto new cards, and sell the result. Send your cards to:
St. Jude's Ranch for Children
Card Recycling Program
100 St. Jude's Street
Boulder City, NV 89005