For some strange reasons, I want to write HTML directly to the Response stream from a controller action. (I understand MVC separation, but this is a special case.)
C
You can do return Content(...); where, if I remember correctly, ... would be what you want to write directly to the output stream, or nothing at all.
Take a look at the Content methods on the Controller: http://aspnet.codeplex.com/SourceControl/changeset/view/22907#266451
And the ContentResult: http://aspnet.codeplex.com/SourceControl/changeset/view/22907#266450