Music Theory
Music theory.net: The Minor Scales
Listen and learn with this explanation of minor scales. Each description of harmonic, melodic, and minor scales provides an illustrated example, and audio clips.
Music Theory
Music theory.net: Key Signature Calculation
An explanation of key signature calculation for advanced music students. Discusses the use of sharps and flats in music composition, with illustrated examples. (You may need to download Flash player to view this site.)
Music Theory
Music theory.net: Scale Degrees
A thorough explanation of scale degrees and the various names for each note. Provides illustrated examples and audio clips to enhance the lesson. Terrific resource for music students and teachers!
Music Theory
Music theory.net: Diatonic Triads
Descriptions of diatonic triads: major, natural minor, and harmonic minor. Provides animated illustrations, and a printable chart at the end of the lesson.
Other
Dr. Brian Blood: Music Theory and History Online
An exhaustive resource with everything concerning music theory. From ear training to music history, this site covers it all.
Other
Music Theory First Aid for Struggling Students
This site provides music theory information on such topics as rhythm, intervals, scales, chords, etc. Also, there is a fine section which describes the basic concepts of form and structure.