Just discovered copyrightfriendly.wikispaces.com!
I like their comprehensive lists of copyright-free resources so much that I pasted three of the lists into our school library's website, under Technology (with credit given).
Public Domain Images and Sound
Copyright-free Music and Audio
Image Generators and Clipart
These sources are GREAT for student (and teacher) media projects, papers, wikis, blogs, etc.
No wonder the site is so robust -- its author is Joyce Valenza, super star librarian! Thanks (AGAIN), Joyce!