The Creative Commons Initiative
The Creative Commons is one of the most exciting public domain initiatives in recent times which is based on the idea of a positive right to the public domain. It allows people to choose various licenses granting, rather than taking away freedoms which copyright normally does. Do have a look and if you feel inspired, join the open content party.
For an introduction to the idea of open content licensing please have a look at "Guide to Open Content Licenses"
One of the most important advocates of the public domain has been Lawrence Lessig who has been writing and speaking about about the excesses of copyright in different public forums. His latest book Free Culture traces the history of copyright and creativty in the United States. The book can be downloaded for free at http://www.free-culture.cc/.
For a power point presentation that introduces the world of open content click here