Believers will tell you that the Aztec Sunstone calendar comes to an end on the 21st of December, 2012. But before you go and buy that Ferrari, or pack your family up for the survivalist cabin in the woods, please consider the following.
By believing in this, you are taking as truth information from people who believed dirty, unwashed Spaniards were gods just because they had a couple of guns.
A NASA scientist has this to say:
http://www.space.com/video look for 21-12-12 Just another day.
Finally, please note that the sunstone is a circle. A circle has no end. The cycle just repeats.
But you should plan the party. We need more excuses to do that.