The fun part about the 21st prediction is that the MAYANS do not think the world will end on that date. The calendar does NOT end on that date, its is just the end of what they call the "long cycle" and then their calendar resets. It is not that different then the Dec 31st/Jan 1 date roll over that the western calendar does every year...
But never let facts get in the way of a good end of the world party I say!