The National Archives and Records Administration (NARA) is an independent federal agency that preserves the nation's history and oversees the management of all federal records. A few important links are:
These are not traditional libraries, but repositories for preserving and making available the papers, records, and other historical materials of American Presidents since Herbert Hoover. (From the National Archives)
"Smithsonian Institution Libraries is the most comprehensive museum library system in the world, supporting the vital research of the Smithsonian, as well as the work of scientists and scholars from around the world."