This website provides strong beginning to advanced lessons in fundamental Music Theory concepts. The site provides a wonderful array of tools, lessons, and exercises that can help with providing a foundational basis of music theory. The site has been cleaned up and polished to allow the most user-friendly interface that I have come across in some time. As a music instructor, this site can be used for many different learning levels and help provide supplement to any music course.
The lessons stretch from basic music theory to advanced part-writing and ear training. It also has lessons incorporating the piano and guitar, truly making this a must-use site for music educators.