The Library of Congress is the largest library in the world, with millions of items in its collections, including:
Enter your search terms in the box at the top of the search results page, select any limiters (the Formats, Dates, Sites and Collections, Contributors, Subjects, Locations, or Languages, options on the left side) that seem appropriate, and click "GO".
Additional ways to search the vast collection of the Library of Congress include:
Whenever possible the Library of Congress provides factual information about copyright owners and related matters in the catalog record for each item, or in the text that accompanies a collection. The Library generally does not own the copyright and it cannot grant or deny permission to publish or otherwise reuse material in its collections. Permission and possible fees may be required from the copyright owner independently of the Library. It is your obligation to determine and satisfy copyright or other use restrictions when publishing or otherwise distributing materials found in the Library's collections. Transmission or reproduction of protected items beyond that allowed by fair use requires the written permission of the copyright owners. Researchers must make their own assessments of the applicable rights in light of their intended use.
Many of the items available online from a Library of Congress collection were originally created decades or even centuries ago. Lolly Gassaway provides a useful chart on When U.S. Works Pass Into The Public Domain. The relevant date for a recording is when it was made, and not when the music was written. Digital copies of recordings and images have two copyrights - the one held by the person who created the original recording or image and one that exists from when the digital version was created. Many of the digital versions of items in the Library of Congress collections were made by Federal employees and are therefore excluded from copyright, or they were made to be distributed.