All of my work is licensed under the CC BY-NC-SA 2.0 license. It sounds scary, but it's not actually so bad. Essentially, it means that you can use anything I make under three conditions:
I believe in a world where everything can be remixed, transformed, and built upon. I think that an open-source, collaborative, and iterative approach to things fuels innovation. Unfortunately, traditional copyright is incredibly restrictive. I'd love to see all the unique and interesting ways people build upon my work, and the licenses offered by Creative Commons ensure that people can do just that (without any legal pushback.)
Don't get me wrong: the public domain is both great and important. It ensures that the important stories of our time can be remixed and iterated. However, for someone who is still alive and actively making things, it doesn't quite work out. The license I chose guaraantees that those creative freedoms are available, while also ensuring that people can't sell what I make for a quick buck, and also that credit is given where credit is due.
Again, I believe that our world might be a little more utopic if we could iterate and remix everything. By using a ShareAlike license, I can ensure that all derivitave works must also let people derive from that. That way I can create, and everyone can iterate, and iterate, and iterate (et cetera, et cetera.)