Found this via a search for a "free printable Advent Calendar". Turns out the article is intended as a resource for Latter Day Saints, but the printouts are simply for a general, cute all-purpose scene intended to be put together piece by piece a day at a time from December 1-24. You can print out a full-color version, or a blackline version you (or your kids!) can color yourself (pdf files -- Update: tried to link directly, but both links were oddly redirecting somewhere else, so I removed them).
It's a nice size for a bulletin board or flannel board display -- the Wise Men, for example, are just under 6" tall. If you printed them out on magnet paper, they'd be a fun addition to the refrigerator door, too! :)
We'll have our usual Jesse Tree and Advent Wreath activities going, of course, but I thought it would be fun to have a simple Nativity Scene coming together day by day, too!
Here's a link to a picture of the set assembled in full.