The Powerhouse Museum in Sydney Australia is a kind of "everything in the whole wide world" museum built off of the collections acquired for Australia's 1879 international exposition. (This model for museum building is reflected in the US in Chicago's Field Museum.)The museum's mission is broad-reaching: "The Powerhouse Museum develops collections and presents exhibitions and programs that explore science, design and history for the people of New South Wales and beyond."
As the online presence for such a broad institution, the museum's website, http://www.powerhousemuseum.com/ , is more of a clearinghouse for public historical, and more contemporary public knowledge than a more typical single-topic-focused public history website. From the powerhouse museum's website, it is possible to access information about Australia's Estonian immigrants, Princess Diana, the 2000 Sydney Olympics, and the history and material culture of menstruation among others.
Beyond its eclectic access points, the Powerhouse Museum's website is making waves in the museum world because of its experiment with social tagging in its online collections database. To view the Powerhouse's user-generated tag-cloud go here: http://www.powerhousemuseum.com/collection/database/browsekeywords.php
Overall, I would rate the Powerhouse Museum's website 5 earths, based on the thoroughly considered website review system published by the Public History Resource Center. I believe it can serve as an example for a comprehensive learning center online. What is may lack in depth in certain areas, it makes up for in breadth and interest piquing.