I really enjoy seeing gaming materials released with Creative Commons licenses. Here are a few I was part of.
108 Terrible Character Portraits
This was a Kickstarter project I organized with artist Jeff Preston to create a bank of character portraits that could be used by anyone, for anything, as long as they cited the source. (Released CC-BY. License details in the zip.)
Want to see what they all look like? Check out the Gallery
Here’s a little sample: