Interestingly enough, for all the talk about 2012, it is quite difficult to find a simple listing of all the prophecies.  Most of what you find on the Internet is vague–generalizations of mass destruction or a transformation into a new age.  I was able to find a couple decent sources, so I have listed them below.

http://www.onereed.com/articles/katun.html

http://www.sacred-texts.com/nam/maya/cbc/index.htm
(this is a link containing the Chilam Balam, a book of prophecies)

It appears open to interpretation as to whether 2012 will bring total destruction or a transformation of our world.  So, below are prophecies (not necessarily Mayan) for 2012:

1. There have been three or four previous races and ages of humanity (depending upon the source you read).  All of these have been destroyed in major cataclysms.  December 21.2012 marks the end of this age and it will end in major catastrophes such as Earthquakes.  (see commentary on this statement below)

2. For half of the katun (20 year Mayan cycle) there will be food, for half some misfortunes. This katun brings the end of the "word of God." It is a time of uniting for a cause.

3. As we pass through transition there is a colossal, global convergence of environmental destruction, social chaos, war and ongoing Earth changes.

4.  The Earth will undergo a magnetic field shift, reversing the polarity of the planet.

5.  An asteroid or comet will collide with the Earth.

For now, this is all that I am listing as I come across so many vague statements I do not feel comfortable listing them for others to read.  As I continue with my research, I will add to this list when appropriate,  If anyone would like to offer me sound information, please email comments@2012endofdays.org.  Please include the source of your information so I can validate.