The Friend usually has some sort of countdown, and we've done several over the years. Here's the link to this year's version.
In 2008 I did another blog post countdown - the year Weston was 25. Here's the link to his first Christmas picture. I'll try to remember to add the 2008 link each day this year!
Wrapped Books. Our kids were older before I learned of this tradition, of wrapping 24 books and opening one each night and reading it together, but we tried it anyway and they loved it. In order to come up with 24 items without buying anything, I added some Christmas movies to the collection. That was fun.
If I ever find a picture of our actual felt tree countdown, I'll switch it out, but that's what we did for years and years and years.
What's your favorite Christmas Countdown?