Music

allmusic.com http://www.allmusic.com/ A massive database including every genre of music, searchable by artist or composition. Also includes informative essays, biographical information, reviews, and musical sub-genre guides listing essential artists and recordings.

American Music Center http://www.amc.net/ A non-profit music information and resource center.  The homepage provides links to information regarding opportunities, grants, membership, publications, news, artists and other organizations.
emplive.org http://www.emplive.org/ Actual and virtual museum with permanent and featured online exhibits, which range from oral histories of musical legends to educational music instruction topics.
G Major Music Theory http://www.gmajormusictheory.org/index.html An entire lesson in music fundamentals, music dictation, and analytical listening, designed by a University of Pittsburgh music professor. Listen to music samples, and follow along with free downloadable PDF worksheets and exercises.

History of Banned Music http://ericnuzum.com/banned/ An online chronicle of popular music that has been censored, banned, suppressed, or altered against the wishes of its creators and intended audience.

Internet Public Library http://www.ipl.org/div/mushist/ Internet Public Library Music 102: A Guide to Western Composers and their Music from the Middle Ages to the Present.
Learning Music Theory http://www.emusictheory.com/learning.html Test your music theory skills with free exercises and drills, and explore links to other free resources for music students and instructors.