The Digital Public Library of America

The Digital Public Library of America is a service which attempts to bring together the digital collections of American libraries, archives and museums via a single search portal. The DPLA project is similar in scope to TROVE in Australia and Europeana in Europe.  
The DPLA acts as a giant metadata store, directing clients via the search interface to the institution which holds the original digital work.  At present there are approximately 2.3 million records, although the ultimate goal is to provide access to over a billion items held throughout American cultural institutions.    
The DPLA has a number of 'content hub' partnerships with key cultural organisations, like the Smithsonian Institute, and is also actively working at a grass roots level to uncover and expose local community digital collections.   
If you are interested in learning more about the DPLA project the latest episode of, This Week in Libraries provides an interesting interview with Dan Cohen (the  Director of DPLA). 

TWIL #98: Dan Cohen (Director of the Digital Public Library of America, DPLA) from Jaap van de Geer on Vimeo.