First, head over and check out Wreaths Across America and find out how you can help them lay wreaths on military graves this Christmas. It's takes place on December 15 so you don't have a lot of time. Also, please spread the word and let others know.
Second, if you're planning on sending cards to wounded service members beware because there's hoax going around in an email. If you get one informing you that you can send cards to "Any Wounded Soldier" at Walter Reed, ignore it. It's fake. What you can do, however, is check out the Red Cross site Holiday Mail For Heroes.