Other
Music History Online: Music of the 20th Century
This page covers a wide range of topics concerning 20th century music. Included are many references to styles and composers and terms found in 20th century music.
Internet History Sourcebooks Project
Fordham University: Modern History Sourcebook: Music and Nationalism
Fordham University provides college-level reading on how the Nationalism of the 19th Century affected the music of the 20th, especially Classical music. These composers lived most of their lives in the 1800's, but are often classified...
Other
Music Under Soviet Rule
Historical information and composer information both appear here with reviews of CDs and purchasing links. Point of view is clearly anti-Soviet.
Other
Oculus Magazine: Early Jazz
Written for an audience accustomed to rock, this is a good history of Jazz, from the late 1800's, when the form supposedly took shape, to recommended recordings and books.