The University of Washington Libraries Digital Collections "features materials such as photographs, maps, newspapers, posters, reports and other media from the University of Washington Libraries, University of Washington Faculty and Departments, and organizations that have participated in partner projects with the UW Libraries. The collections emphasize rare and unique materials."
There are a lot of useful resources here--check out the Special Collections section for seventy-five wonderful digitized collections such as Alaska-Yukon-Pacific Exposition Photographs, Centralia Massacre and the Industrial Workers of the World Collection, 1912-1932, and the Vietnam War Era Ephemera Collection (from which the John Wayne poster featured here is taken.)
Good collections descriptions accompany all the collections and some have considerable additional material. American Indians of the Pacific Northwest, for example, has introductory essays, maps, and "bibliographies and links to related text and images as well as study questions that K-12 teachers may use as they develop curricula in their schools." They also have a blog to help users keep up-to-date with changes in their digital collections.
As wonderful as the site is, it could be more interactive. The images are difficult to download and save (which may be a feature rather than a bug!) and there is no Web 2.0 interaction. There is not even a way for users to flag an image that is obviously misidentified.
(Image: Cropped detail from John Wayne in No Substitute for Victory, created by the "Greater Seattle TRAIN Committee (To Restore American Independence Now)" and "Students for Victory in Viet Nam, Seattle Committee.")