Googlelabs have a new search facility in image search, which is similar images. If you click on the similar images link below an image it will display the images which is like that.

similar images @ googlelabs

Another one is TinEye, this will allow you to upload an image and find similar images on the web. From the website

TinEye is a reverse image search engine. You can submit an image to TinEye to find out where it came from, how it is being used, if modified versions of the image exist, or to find higher resolution versions. TinEye is the first image search engine on the web to use image identification technology rather than keywords, metadata or watermarks

TinEye reverse image search