Yotophoto
The first internet search engine for finding free-to-use photographs and images. You can refine the search by image size, orientation and the quite brilliant colour. What they say:
Our goal is to help people locate, remix and republish open and copyleft images. We aren’t just about ‘free stock photos’ for designers, but also about helping educators, bloggers and digital artists find photos they can use without fear of “the man”.
Now stock.xchng is good and until now my main source but…
We (Yotophoto) index various sources of free imagery on the web including Flickr, Wikipedia, Stock.Xchng, Morguefile, Pixelperfect Digital and OpenPhoto.
Go try Yotophoto. It rocks.