Music
Popular Music and Jazz Reference Sources

• AllRecordLabels.com -- "a comprehensive listing of over 9200 record labels indexed by genre, format, and location." Check out its companion sites as well: Publishers Catalogues, Libdex, and the Weblog Compendium.
• Archives of African American Music and Culture
• Biographies of Jazz Musicians
• Center for Black Music Research--The Columbia College Chicago Center for Black Music Research documents, preserves, and disseminates information about black music in all parts of the world.
• Dismuke's Virtual Talking Machine -- includes audio recordings from 78-rpms from the early years of the 20th century. 
• Emplive.com: Experience Music Project -- created by Paul Allen, this site is a museum of sorts which covers the history of music over the last century, which includes interviews with rock, hip hop, etc... artists. 
• Folk Song Database--The Digital Tradition is a searchable data base containing the words and music to over 6500 folk songs.
• History of Country Music
• Lyrics.com
• Jazzgram -- interviews, reviews and more. From the Jazz Institute of Chicago.
• MyMusic.com -- search by keyword, genre or location. Listen.
• National Jukebox LOC -- "The Library of Congress presents the National Jukebox, which makes historical sound recordings available to the public free of charge. The Jukebox includes recordings from the extraordinary collections of the Library of Congress Packard Campus for Audio Visual Conservation and other contributing libraries and archives."
• A Passion for Jazz -- commentary, history, posters, and lots more.
• Recorded Sound Reference Center -- "provides access to the commercial and archival audio holdings of the Library of Congress. The collection dates from 1926 when Victor Records donated over 400 discs to the Library's Music Division to supplement its print and manuscript holdings. In the custody of the Motion Picture Broadcasting and Recorded Sound Division since 1978, the collection has grown to include over 2 million items encompassing audio formats from cylinders to CDs"
• Red Hot Jazz Archive--sound files, essays, discographies and more on artists and bands before 1930.
• Rock and Roll Hall of Fame--read all about the inductees, and, if your plug-ins permit, listen to samples of the 500 Songs That Shaped Rock and Roll.