LoremFlickr

LoremFlickr provides placeholder images for every case, web or print, on almost any subject, in any size. It's simple and free.

Just put the custom url in your code like so: <img src='http://loremflickr.com/320/240/' />

Photos come from Flickr and have a Creative Commons license. The flavor of the license is shown in the top left of the image. The name of the image and the author are shown in the bottom left.