PicsLikeThat - This is a visual and semantic image search system finding images on Fotolia.
Yandex.Images - search for images on the internet, search by image
IQDB - Multi-service image search
lingvist.info - News & Books
isk-daemon - isk-daemon is an open source database server capable of adding content-based (visual) image...
Image Search Options - Download Image Search Options for Firefox. Image Search Options provides a set of highly customizable reverse image search context menu options.