Browse by Colour

labs.ideeinc.com/multicolr
Search 10 million of the most “interesting” Creative Commons images on Flickr by Color
labs.ideeinc.com/multicolour
Search 3 million Alamy Stock Photos
images.google.com
Search Google images by color (green).

Browse by your uploaded image

labs.ideeinc.com/upload

Browse by color/texture/similar images

tiltomo.com
tineye.com
Upload an image and Tineye will find all lookalikes

similar-images.googlelabs.com
Find an image by keyword and than you can view the images that look the same. made possible by Google Labs similar images.

Browse by faces

exalead.com
add imagecontent:Face to your search query at Exalead and the results will only show images of faces. This also works at google images under advanced image search. Try: images.google.com/einstein

Browse by related tags

forestandthetrees.com/findr/findr.html

Browse by Geographic Location

woophy.com
flyr.whatfettle.com
panoramio.com