Multicolr Search Lab - Idée Inc.
A beautiful use of the Flickr API that allows you to browse photos with a colour picker.
polaroiderizer - a slideshow from your flickr tags
A great little Flickr slideshow from Phil Hawksworth.
Related links
Flickr: The Commons
Here's a fantastic collaboration with the Library of Congress. We are being asked to collectively tag historic pictures with no known copyright restrictions. Wonderful idea! Are you watching, British Library?