Adobe Photoshop Lightroom
This module exposes Creative Commons fields in the metadata pane inside the Library module and then allows those data to be inserted into an image's XMP on Export. It is currently under development. If you are interested in helping beta test, please drop me a note. I am especially interested in hearing from Lightroom Version 3 users and Mac OS X users.
I have decided not to pursue this development. Rather, I highly recommend Jeffrey Friedl's Creative Commons Lightroom plugin. I use this myself and, like all Jeffrey's work, it works as advertised!