Firstly, the Mayan calendar does not 'end' in 2012. It just begins a new long count. Mayans added the long count because their previous calendar was reset in too short of an interval. They instead devised an addition to it to encompass all of their history. However, as all of their calendars are circular, it too will simply reset on or about December 12, 2012.
To Mayan's we are in the 4th time this long count has reset to zero. Each time it resets that year is full of calamity. However, the year of calamities happens every so often, this is compound during a reset of the long count. So the idea isn't that the world will end, but that something globally bad will happen.
Furthermore, there are plenty of Mayan writings and predictions that go way past 2012.
To read more go to:
http://en.wikipedia.org/wiki/Mesoamerican_Long_Count_calendar







