A search engine that can filter for only CC images on Flickr but pulls commercial images into the search results from their affiliates ie shutterstock and depostfiles. This site is loaded with commercial feeds which are hard to distinguish from the free stuff at first. Make sure you turn on the Creative Commons filter otherwise you will just get commecial images.

The results are presented with the various image sizes you can download in along with an attibution snippet already filled in, but nite it has compfight in it so a quick alteration will be required