Most of you may have checked this out already, but I recently stumbled across it. It is a good quality live video stream of the Old Faithful area in YNP. Go to the following link and click on the "Old Faithful Streaming Video".
http://www.yellowstone.net/webcams.htm
Someone somewhere is able to control the camera, as occasionally it will pan the area, zoom in on buffalo in the distance or a young lady walking down the boardwalk.