An online photography school run by Photoflex (manufacturer of professional lighting equipment). It currently offers 100 courses, but keeps adding new courses every month.
The school is designed for anyone who wants to become a better photographer, whether a professional or an amateur.
Several of the courses are free (though you need to register online). $45/year grants unlimited access to all the courses offered. I have just discovered it, so I cannot comment on the quality of the instruction, though my first impression is very good, and I intend to check out at least the free courses.
It is at http://www.webphotoschool.com/.