There are literally thousands of courses and degrees you can earn through online colleges and universities. However, music is one of those subjects that doesn't really translate well to learning online - until recently.
Online University.com posted a list of 50 different articles and courses offered in the field of music. NO, none of these will make you a better performer. You really need face to face contact for improving your performance techniques. They do offer a lot in the realm of music history and appreciate. There are even some graduate level courses.