Creative Commons is a nonprofit organization that facilitates and advocates for people sharing their intellectual work, consistent with copyright laws. They provide free licenses and other legal tools to allow creators and consumers to share, revise, use commercially or in other ways distribute their content.
Here are some links to Creative Commons and information about how they work:
January 2010 update on Creative Commons commitment to OA in education
http://net.educause.edu/ir/library/pdf/ELI7023.pdf
UMichigan talks about using Creative Commons