Harold, a suggestion of yours some time ago led me to the CC search on Flickr. Fiddling around, I found a way to search for CC / commercial use / adaptation images (I needed that for a client project). I then dragged the URL onto Firefox's toolbar so I can hit that combo any time I want. This is it:

http://www.flickr.com/search/?q=&l=commderiv&ss=2&ct=3&w=all

You should still check the license, in case someone has an oddball requirement for acknowledgement.