Music Composition
Free advice on how to compose classical music. Free papers and courses by Rowy van Hest.
Music theory
Music Notation and Terminology, by Karl W. Gehrkens
Musipedia
A search engine for tunes and musical themes and a collaborative music encyclopedia. Only the melody needs to be known to search Musipedia or the Web. The melody can be played on a keyboard or whistled or sung to the computer. The Musipedia collection is editable by anybody, just like Wikipedia.
Teroria musical
Web site dedicated to the study of Music Theory. Articles, reference, interactive exercises.