Last month I took the Illustration Master Class in Amherst, MA. There were 70 students and our instructors were Boris Vallejo, Julie Bell, Donato Giancola, Rebecca Guay, Dan Dos Santos, Scott Fischer and Gregory Manchess (a.k.a "Ravenwood"). The course was a week long, with classes starting at 9am and ending at midnight, though often we worked on our projects until 3am. We got plenty of one on one time with each of the instructors. I was sitting next to Julie Bell throughout the week, and right behind Boris, so we struck up a friendship and have stayed in touch since. It's weird, because I was never much of a fan of their work (my own style is closer to Rebecca's), but I really gained an appreciation for their skills while I was there, and I learned A LOT from them. You can see my photos of their work and the class here:
http://www.flickr.com/photos/27980171@N03/
Enjoy!