Given the following associations: [ download_types --> downloads --> downloads_products <-- products ], I create a query (in download.rb) that will list all downloads for a given product ordered by download type.

_downloads.html.erb

<% @downloads.group_by(&:download_type).each do |download_type, downloads| -%>
<h3><%= download_type.name.pluralize %></h3>
<ul>
	<%= render :partial => 'support/download', :collection => downloads %>
</ul>
<% end -%>

download.rb

class Download < ActiveRecord::Base
  belongs_to :download_type
  has_and_belongs_to_many :products
  
  def self.get_by_product(id)
    all(:include => :download_type, :joins => :products, :conditions => ['products.id = ?', id], :order => 'download_types.position, title')
  end
  
end

support_controller.rb

class SupportController < ApplicationController
  
  def downloads
    begin
      @downloads = Download.get_by_product(params[:id])
      render :partial => 'support/downloads'
    rescue ActiveRecord::RecordNotFound
      render :text => ''
    end
  end

end