ICYMI: Citizen DJ - free-to-use samples from the US Library of Congress for remixing
The Citizen DJ project invites the public to make hip hop music using the free-to-use audio and video collections from the Library of Congress. By embedding these materials in hip hop music, listeners can discover items in the Library’s vast collections that they likely would never have known existed.
Also check out the interactive exploration tool which lets you browse the samples in your browser, and the bulk downloads which let you download the full .WAV archives.