I have taken a few online art courses, not many, but a few. Mostly to get myself kick started, or to pick up a new technique. I have gone on one week art courses in London, which was very very cool, but I have to say, for the sheer bang for buck, no that's not even fair, simply I am taking an absolutely brilliant course, and I have to share.
It is offered by MOMA, yeah, the Museum of Modern Art in NYC and the course instructor is an artist and a conservator of modern paintings, as in he repairs and maintains the ones at MOMA.
There is SO much information provided and at such a high level I am blown away. There are at least 20 hours of video (I think more, I'm only part way through) divided between art history and studio technique. From the basics of how to stretch canvas, what makes up paint, how to play with it, and the techniques of 8 of the NY Abstract Expressionists, who if nothing else, pushed the boundaries for what you can do with paint.
It's a little pricey, $US 200, (less if you're a student or teacher) but I've paid half that for a WHOLE lot less. There are specific tasks for the students to do in their studios to practice some of the techniques. If you want to pay twice as much you can email back and forth and do chats and forums and send in work for evaluation with the instructor...I didn't feel like it and it is TWICE as much......ooops, sorry, I'm too late, the guided option is sold out, but you can still do the self-directed, find it here: Materials and Techniques of Postwar Abstract Painting, Self directed.
I'm a big girl now, I can play on my own, but this resource, I SO had to share. Three thumbs up.