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.
University of Oxford (UK)
Oxford University: Rupert Brooke
This marvelous site provides, in addition to an informative biography, an obituary by Winston Churchill, "The Dead" (a poem by Brooke) with helpful notes, and links to a number of other poems like "Treasure" and "The Soldier."