Flickr: The Commons
Collaborative project between Flickr and the Library of Congress (and hopefully other institutions in the future) to share and tag public domain images. Currently 3000 images from the Library of Congress collection are available.
CyberBee
The Adventures of Cyberbee are lessons and curriculum resources for using primary sources in K-12 classrooms. Includes some copyright lessons too.
University of Minnesota Libraries -- Copyright Initiatives: Fair Use Analysis Tool