I recently wrote about the GNU Public License (GPL). All of my software that I write on my own will most likely be licensed by GPL so others can use and modify it freely. I really think this benefits society.
What about content, such as text, image, audio, or video? Analogous to the GPL, there are the Creative Commons (CC) licenses. CC is plural in that there are many licenses available, depending on how the author wants to share his or her work. The core right is to be able to redistribute a work for non-commercial purposes without modification. I believe the most popular variant is the Attribution-NonCommercial-ShareAlike 3.0 Unported, of which my Super Nerdy Cool blog is licensed with. I should remember to always post communicate the license of all my work (such as presentations, lecture notes, etc.). Examples of how to attribute can be found here
Now, onto some resources.