Hey, check it out -- The Scream, by Edvard Munch, seems to have been found. It is currently being studied for authenticity, but authorities seem to be pretty certain that it's the real deal. Not a whole lot of details, so far, but you can listen to the report at the link above for more info.
I love that painting! And, if you look at it in a historical context, it's a pretty impressive piece. This painting is of the Expressionist period, during which time artists started painting images of emotions rather than scenic or narrative compositions. This was a major shift in art.
This painting is probably as well-known as the Mona Lisa. I use it a lot in my classes and often use it when demonstrating Photoshop because you can have so much fun with it. It can evoke so many emotions, and yet you don't really know why the poor guy (girl?) is screaming. But everyone can identify with it. We've all felt that way.