http://www.myngle.com/
I thought this was interesting. You basicaly can research and choose the teacher that you think would best meet your needs. Some teachers offer free introductory lessons to attract students and teachers set their own price for each lesson so there is competition for students. I thought it was a good example of a way in which the free market solves the problem of education in a stateless society(ie the internet) This particular site is for people trying to learn languages but i dont see why it could not be applied to other fields of study.
http://tentativemind.blogspot.com/