Xbox Live Marketplace has been running Deal of the Day promotions since Friday; today's is completely free. Pick up a New Year's Theme for the rock bottom price of zero Microsoft points.
There it is, pictured above. The free offer is good through the end of today, but I believe that clocks in at Pacific time, so it means folks on the U.S. east coast have to 3 a.m. if they want it. However, yesterday's Deal of the Day, Worms 2: Armageddon for 400 Microsoft Points, was still live when I posted this at 6 p.m. Mountain time. But the 2010 Avatar party glasses had gone back to 40 MS points. So who knows.
The DotD promos - which Microsoft is not announcing in advance - last through Dec. 31, and if you're keeping track of this sort of thing, Cheap arse Gamer has been archiving the giveaways here.
Kotaku AU Note: Sorry guys, it appears this offers only applies in the US.