My fiancee and I are sending handmade christmas cards to the troops. She is a third grade teacher so she is having her kids, and is going to approach every teacher in the school to have their kids make a card. I also sent out a company wide email where I work for my co-workers kids to participate. I'm expecting to be able to mail up to 500 cards by next Friday so, hopefully, they'll be received in time for Christmas.
If you do this make sure you have a soldier to address them to. My ex manager is currently in Baghdad so I'm sending them to her to distribute.