A good site for music theory, notation, and ear training

Web site dedicated to the study of Music Theory. Articles, reference, interactive exercises. Most of us probably already know this site but its nice to have on hand and incase you haven't worked with it, its great for ear training.

A one-stop, comprehensive, non-profit resource for parents, students, teachers and fans of the piano, with over 1000 pages of free, non-commercial information, operated as a public service since 1995.