I stumbled across quite a nice resource the other day, a site called Everystockphoto.com. The canadian-based site is essentially a license-specific photo search engine, currently indexing 4,458,956 free photos from a variety of sources (though flickr seems to be one of their main source targets).
What I do like about them in particular is the fact that they integrate so many sources into a single search result, have a nice clean and modern interface and in particular, have taken it a further step by having user accounts that allow you to build up collections, add metadata to image results and gain access to a fairly vibrant forum community.
The site is simple, easy to use and proves to be an invaluable asset when looking for decent quality, free stock images to use in your projects.
Though don’t just take my word for it, rather check it out at http://www.everystockphoto.com
Related link: http://www.everystockphoto.com