Whichever calendar you choose, you will need to figure out the "gift" for each day. The tradition has been a chocolate or trinket, but more and more people are using simple activities the whole family can enjoy.
Here are some examples: read a holiday story, make hot chocolate, send cards to grandparents, make cookies, see holiday lights, visit Santa, make gingerbread men/women, decorate the tree, make gift tags, sing carols, go ice skating, make a popcorn garland, watch a holiday movie, make an ornament, write letter to Santa, put on a play, make luminarias, hang mistletoe, stargazing, etc. You get the idea.
And now to our calendars!
A simple paper chain can be used as an advent calendar. Make 24 loops and have your children tear one off each day. It's so easy, the kids could make it over Thanksgiving weekend. You can write the activity on the inside of each loop. Making one out of fabric with velcro would be great to keep for next year.
A super easy cardstock calendar. Cut out rectangles and fold them in thirds. Write the activity inside and seal with a sticker. Hang them from a ribbon with clothespins or on a garland like here:
A basic calendar could be made of felt and have pockets to hold small toys, candy, or activity cards.
This one is made of paper, but I think I'd rather do it in fabric so that it would last until next year:
This is a unique one.
This is also different -- you could really use any container.
A printable calendar.