PicSearch – Image search with some interesting options; for example, you can choose to search only black and white or color photos.
YotoFoto – A search engine which claims to be indexing over a quarter million Creative Commons, Public Domain, GNU FDL, and various other ‘copyleft’ images.
Google Image Search – A resource so commonly used it doesn’t need a special explanation; still one of the best ways to find images of any kind on the web.
Pixsy – Image search engine that’s striking a lot of partnerships. Also provides PixsyPower, a custom video and photo search for your own site.
StockPhotoFinder – A search engine specialized in finding stock photos.
EveryStockPhoto – This site is indexing over 1 million completely free photos from various sources.