Today is Public Domain Day 2013.
From the CSPD Web Page:
What is entering the public domain in the United States? Nothing. Once again, we will have nothing to celebrate this January 1st. Not a single published work is entering the public domain this year. Or next year. In fact, in the United States, no publication will enter the public domain until 2019. Even more shockingly, the Supreme Court ruled in 2012 that Congress can take back works from the public domain. Could Shakespeare, Plato, or Mozart be pulled back into copyright? The Supreme Court gave no reason to think that they could not be. And wherever in the world you live, you will likely have to wait a very long time for anything to reach the public domain.
Over on the Creative Commons Blog, Timothy Vollmer has a link-rich post looking at some of the material entering the public domain in other parts of the world and resources to access materials already in the public domain.
See Also: World Copyright Terms Map