There are just way too many art videos on Youtube to narrow down to one or two. I guess it depends on what a person is looking for. For drawing instruction I like Proko and Jeff Watts. For painting, too many to mention. If you just want to watch some good demos, I love to watch Mike Lang. He has a ton of demo videos, some of which are over an hour long. If you can't learn something from watching him for an hour, I don't know what to tell you.