The Planetary Society is letting you have your name sent to Mars for free on Phoenix. Your name will be included on the Phoenix DVD and Visions of Mars. Plus, you get a neat little printable certificate, a nice last minute gift. The offer lasts until January 5.
While you're at it, send a message to the moon with Japan's latest lunar mission, SELENE. A dandy certificate is also available for this message. Deadline is January 31 for inclusion.