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Stanford University
Ccrma: Common Music Notation
This resource features information on notes, rests and many, many other basic music theory examples.
Other
The Basics of Reading Music
This site is an overview of how to read music. The basics of notation such as note and rest values, the names of lines and spaces of both treble and bass clefs, etc. are covered. Includes downloadable audio files.
Other
The Tonal Center/diatonic Scales
A comprehensive summary of basic music theory. Commentary is thorough yet practical. Information on tonality, chords, scales, cadences, etc. This pages is on diatonic scales.