Hey, want to do something nice while you clean up after Christmas? St. Jude's Ranch for Children accepts used Christmas cards, from which the children make recycled cards by removing the front and attaching a new back. (The fronts can't have any writing on them, obviously.) They then sell the cards to help support the ranch. You can send cards to this address until February 28:
St. Jude's Ranch for Children
Card Recycling Program
100 St. Jude's Street
Boulder City, NV 89005
Also, you can order cards from them for next year!