OpenClipArt.org is a great portal containing a lot useful contents for course designers.
It would be useful to have direct openclipart repo plugins allowing you:

• search commons
• import media into course local files
• auto meta-info support (licence, source URL etc.)

See: http://http://openclipart.org/
some code samples : http://openclipart.org/wiki/Tools
and : http://code.google.com/p/clipartbrowser/

They have an API now: http://openclipart.org/docs/api