Pete Brown is a local guy with a great deal of Silverlight content on his blog, and some cool wallpaper downloads. Pete pointed to the Expression Encoder White Paper today. The document describes itself as providing the "best practices and methods for providing integrated and branded media player skins for Microsoft Silverlight".
After a quick read, I'd say the document does a fine job describing how to build custom skins and templates for the Silverlight media player. The techniques described in the document will also work with the ASP.NET Futures <asp:Media> control. Both of those controls provide additional features (like the standard VCR controls) on top of the Silverlight <MediaElement/>.
The document gets confusing, however, when it describes the class hierarchy behind the player. For instance:
The _Button class handles binding the events and animations to the XAML. The intention is for you to handle the events you are interested in.
See the example above in "Roll your own controls" for details on how to implement your own buttons making use of _Button.
Cognitive dissonance comes into play several times in the document when the text describes how to consume underscored type like _Button. By convention, ASP.NET AJAX prefixes private fields, methods, and types with an underscore. When adding a new button to the player that is not one of the "well known" buttons (like the PlayPauseButton), it feels like a hack to instantiate or derive from an underscored class.
Personally, I've been a bit frustrated at the lack of extensibility in the player control provided by Expression. There are no public methods available to override the behavior of the Next, Previous, and VideoWindow button clicks, for example. I hope the ASP.NET Futures version of the control will flesh itself out a little more in the future.