Only the British Museum could bill itself as the Museum of the World without straying too far into hyperbole. With the fruit of centuries of acquisition (imperial or otherwise) at its disposal, the BM has allied with Google to showcase some its most impressive items online. Users can scroll along an interactive timeline and drill down to objects of interest. Along similar lines to their very successful "A History of the World in 100 Objects" collaboration with the BBC.
This fascinating and graphically striking website maps historical articles on Wikipedia onto a timeline. Viewers can confine themselves to the tiny span of Earth's history that features the human race, or zoom out to the unimaginable expanses of geological time. Incredibly, the project was put together by (very smart) college students.