You can send Holiday cards to service members through the Red Cross at the following address:
Holiday Mail for Heroes
PO BOX 5456
Capitol Heights, MD 20791-5456
Must be postmarked by Dec. 7th!!!
For more info: http://www.redcross.org/support/get-involved/holiday-mail-for-heroes
Snopes says this is the one that works-sending them to Walter Reed does not.