I don't know if this applied anywhere outside of Catholic school upbringings, but Advent calendars were a big part of the lead-up to the celebration of the religious reason for the holiday. Now I see Advent calendars with more commercialized and standard Santa traditions as the themes.
There are two "Advent calendars" on the web now with TV themes. The first one contains news bloopers from an Irish TV network. You can find this at http://u.tv/calendar/.
The other one has a lot more variety when it comes to the individual daily windows, but it all centers around the upcoming Christmas special for 'Doctor Who', "Voyage Of The Damned". You'll find that one at the BBC website homepage for the good Doctor: http://www.bbc.co.uk/doctorwho/.
That one contains clips from the special plus games, puzzles, Christmas cards and behind-the-scenes pictures.