I especially love the ornament one--put each of your favorites on it, or buy NEW ones. I am an ornament whore. The more, the better.
But there are so many fun paper ones to choose from each year. These three are my dream disposable advent calendars:
This lovely Caroline Gardiner calendar
The Moonstruck Chocolates calendar (though I would only pay the asking price of $65 for it if it were full of caramels. I'm just not a truffle person).
And finally, this sweeet whiskey calendar (for only $245!):
And it's cat approved: