If you go to this web site, Let's Say Thanks you can pick out a thank you card and Xerox will print it and it will be sent to a soldier that is currently serving overseas. You can't pick out who gets it, but it will go to a member of the armed services.
It really only takes 10 seconds, and it seems completely free and legit. It only asks you your name (doesn't say first or last, I just used my first), you hometown and state. You get to pick the card and the message.