http://xboxforums.create.msdn.com/forums/t/27849.aspx
This is a great collection of shader tutorials, each of which have example code and a short demo video. Very useful reference material if you are interested in graphics, even outside of C# or XNA, as the code is very easy to read, and the shading techniques are broadly applicable, both to 2D and 3D environments.
Thanks for the share winkio. Shaders have been something I've been meaning to learn about.