www.flickr.com A photo-sharing website that allows users to easily organize their photos in any order they prefer. This is a great tool to teach students how to upload online, and to have them pull photos and information from a source you trust!
CrashCourse on YouTube Six awesome courses in one awesome channel: John Green teaches you US History and Hank Green teaches you Chemistry. Check out the playlists for past courses in World History, Biology, Literature, and Ecology.
The Learning Registry is an open source technical system designed to facilitate the exchange of data behind the scenes, and an open community of resource creators, publishers, curators, and consumers who are collaborating to broadly share resources, as well as information about how those resources are used by educators in diverse learning environments across the Web.
An article by Tasha Squires and Mary Golden entitled "Partnering With the Public Library on Web 2.0 Tools for Student Research" from the magazine Internet@Schools. My portion is under the heading "Research Databases."