The Mayans had a very elaborate calendar that ended on December 21, 2012, effectively predicting several thousand years into the future the winter solstice and a planetary alignment.  The theories I have read an heard about have been quite diverse and range from hey the Mayans got tired and had to find a good place to end their calendar to the world is going to end!  Some of the views have also been positive, though.  Some see this date as the beginning of a new age in human consciousness.  

I recently picked up a deck called the 2013 Oracle.  It is a unique system that spotlights the changes occuring after the winter solstice 2012.  Not coincidentally, the numbers 20 and 13 are integral in the Mayan calendar.

I'm by no means an expert on Mayan history, culture, religion, or the calendar itself.  I'm an enthusiast who finds it pretty interesting.  My own personal view is that the Mayans did a great job in predicting a certain celestial event which in itself will probably be significant in some important way that influences and affects the world.  But, I don't think the world is going to end.  

Anyone who has any interesting theories or specific interest in this topic I invite to give their input.  Also, does anyone have any opinion on the possible connection between the increased incident of crop circles as we get closer to this fascinating date.