One of the standard ideas is practiced by many-Advent Calendars. Traditionally they have a treat like chocolate that you get to claim each day up until Christmas. You can purchase pre-filled boxes or you can find many made-at-home versions such as this great mini bucket board.
Hanukkah does not begin on the same day of the month each December, so unlike the Advent calendar that counts down days until Christmas, the counting here occurs starting on the first day of Hanukkah. There are 8 nights that are celebrated for Hanukkah in the Jewish faith.
There is also another event that some people are choosing to count down to this year: December 21, 2012. Some people believe that this is the date that the Mayans may have predicted that the world was going to end. I'm not sure what type of graphic would portray this type of count down better than a Mayan calendar with a digital countdown attached, but at any rate it is a date becoming talked about with greater frequency.
Lastly, a countdown that means different things to different people is the countdown until the New Year. This is one of my favorites because I am a very symbolic person. I look at the beginning of a day, month, and year as a time that change can begin. The new year means a time that I can pursue a new path and achieve new goals.
What other events do you and your family count-down to?