Music Theory Online
Published six times a year, Music Theory Online (MTO) is the electronic journal of the Society for Music Theory. Each issue includes a target article, book reviews, and reports from a distinguished panel of International Correspondents. In addition, MTO publishes announcements of upcoming conferences and calls for papers, a list of job opportunities, abstracts of recently completed and in-progress dissertations, and summaries of recently published books."

Ricci Adams Music Theory
Animated tutorial to music theory.

Harmony in Tonal Music
Guide to understanding the role of chord progressions in tonal music.

Society for Music Theory
Site for The Society of Music Theory journal, containing links to useful resources regarding music theory.

The Musical Intervals Tutor
A study aid to instruct students on how to learn the sounds of the basic musical intervals from minor second to perfect octave.

ChordWizard: How Music Works
Brief tutorial that covers the basics of music theory.