Creative Commons has made it very easy to decide which of their licenses (currently there are eleven available), and to apply the license to your content.
I’ve added a reference to the new Creative Commons license for the contents of this website to my template; scroll down to the bottom of the sidebar and it’s there. What does this license mean? Essentially it makes explicit the terms under which most bloggers have always made their content available: anyone can copy, distribute, display or perform the contents of the weblog, provided they give me credit. No one can use the contents of my website for commercial purposes without my permission. And no one can create an altered or otherwise derivative version of my website. The full text of the license is also available.