There is an entire guide on locating images, which includes information on copyright and creative commons licensing. Here are a few sites that are good initial starting points.
Note that the CC database is comprised of data from many contributors, and that CC does not verify whether the images are properly licensed or attributed. CC recommends independently verifying the licensing status and attribution information before reusing the content.
Celebrating the public domain "in all its abundance and variety," this online journal includes essays as well as collections of images, books, audio and film.
A subset of Google Images. Images are organized by decade, and searchable in Google using this syntax: xxxx source:life. For example, university of chicago source:life.
Funded by the Duke Endowment "Library 2000" Fund, presents images and database information for over 7,000 advertisements printed in U.S. and Canadian newspapers and magazines between 1911 and 1955.
With Music Online, Alexander Street Press aims to provide the most comprehensive database in streaming audio, video, reference, and scores on the web. Music Online allows users cross search all of the music databases published by Alexander Street Press. Includes Classical Music Library, American Song, Contemporary World Music, Garland Encyclopedia of World Music, Jazz Music Library, Smithsonian Global Sound.
Provides high quality live concerts in a downloadable format. The Internet Archive has teamed up with etree.org to preserve and archive as many live concerts as possible for current and future listeners.
DRAM's collection contains nearly 2,300 albums worth of recordings from a distinctive set of 15 independent labels. From folk to opera, Native American to jazz, 19th century classical to early rock, musical theater, contemporary, electronic and beyond.
Video
There are multiple sources for videos at the Library. The guide to finding films contains more of them than I include here.
The Vanderbilt Television News Archive is the world's most extensive and complete archive of television news. We have been recording, preserving and providing access to television news broadcasts of the national networks since August 5, 1968.
The collection spans the presidential administrations of Lyndon Baines Johnson, Richard Nixon, Gerald Ford, Jimmy Carter, Ronald Reagan, George H.W. Bush, Bill Clinton, George W. Bush and Barack Obama. The core collection includes evening news from ABC, CBS, and NBC (since 1968), an hour per day of CNN (since 1995) and Fox News (since 2004).