HTML comments to tell you what partial is rendering

render_with_comments.rb

# Throw a comment in before and after every render call on html based templates
module ActionView # :nodoc: all
  class Base
    alias_method :render_file_without_comments, :render
    attr_accessor :render_stack

    def render(options = {}, local_assigns = {}, &block)
      self.render_stack ||= []

      if options[:partial]
        path = _pick_partial_template(options[:partial])
      elsif options[:file]
        path = self.view_paths.find_template(options[:file], template_format)      
      end

      self.render_stack.push(path) if path
      without_comments = render_file_without_comments(options, local_assigns, &block)
      parent_render_path = render_stack.size > 1 ? render_stack[render_stack.size - 2] : nil
      if path
        self.render_stack.pop 
        comment_string = "#{path}"
        comment_string += " CALLED FROM #{parent_render_path}" if parent_render_path
      end 

      return without_comments if template_format != :html || options[:without_comments] || self.render_stack.size == 0 || path.to_s[0, 8] == "layouts/"

      "\n<!-- BEGIN #{comment_string} -->\n" + without_comments + "\n<!-- END #{comment_string} -->\n"
    end
  end
end

I like it. Might be cool to put in a timing for the actual call to render. I've started being very judicious with my partials due to performance concerns.