Great news from Gabriel Burt, lead developer for the Open Source media player Banshee:
Search based on the license of a song/album with direct support of displaying CC license logos!
More details available on Gabriel's blog post.
This feature is slated to be in Banshee 1.6 but you can play with Gabriel's development branch which has this feature thanks to the beauty of git.
git clone <http://banshee-project.org/~gburt/banshee.git>
Technical notes of the feature: Gabriel wrote his own parser for extracting the license information from the files. That was needed because there is currently not a Mono port of liblicense, a library which reads and writes license metadata to a wide variety of files. But now if anyone wants to help out and do the port to Mono you have an example of how to access this information via Mono.
Lets keep this ball rolling and get license read/write support in more applications!