Forcing a different render format

I am writing an OAuth system for FilmAmora for the iphone app (and anything else I guess) to use.
I want to always output xml from the controller that is handling the catalog output... but how to do that!

I came up with this:

  def list
    render :template => "/catalogs/list.xml.builder", :content_type => "text/xml"
  end

This will always output xml (with the right mime type) no matter what the requested format was.