Other
Music Fundamentals
This is like a music theory textbook online. It includes great explanations and assignments, although there is not a way to check your completed assignments. It begins with the basics and goes through triads. Midi files are included.
OpenStax
Open Stax: Catherine Schmidt Jones: Key Signature
Learn about key signatures with this well written tutorial. You can test what you have learned near the bottom of the page with a key signature problem. The solution is available with just a click of the mouse.
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
Tone Savvy
You will find many free games that will help you develop your music theory knowledge. Learn rhythmic dictation, key signatures and intervals as well as several other topics concerning music theory.
Other
Theory on Tap: The Circle of Fifth
A nice site that breaks down into three sections: "what is the circle of fifths", "finding key signatures" and "guitar tuning and the circle of fifths."
OpenStax
Open Stax: Catherine Schmidt Jones: The Circle of Fifths
A way of organizing the various key signatures, the circle of fifths is a good tool to help visualize the relationships of the different keys. This tutorial includes several self checking quizzes to test your knowledge.
BBC
Bbc: Music Theory
This resource presents a fun and interactive way to learn all about the elements of music. It offers links to information, definitions, assessments, and examples of melody, harmony and tonality, structure, tempo, metre and rhythm,...
Other
Ruby Cliff Computing: Elements of Music Notation
Fine site that focuses on music notation and on learning how to read it with a focus on the guitar. Includes charts, tips, and other useful information.
Toby Rush
Music Theory: Key Signatures [Pdf]
A music theory worksheet regarding key signatures. Requires Adobe Reader [PDF].
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.
Other
Tone Savvy: E Music Theory
This site provides good online learning games and exercises for music theory. It also has a lot of options for teachers if they choose to subscribe.
Music Theory
Music theory.net
An online beginning music theory and ear training site. This site is for students to use at home to reinforce what they learn in class.