map.resources :clients, :key => :client_name do |client|
  client.resources :sites, :key => :name do |site|
    site.resources :articles, :key => :title
  end
end

/clients/:client_name
/clients/:client_name/sites/:name
/clients/:client_name/sites/:site_name/articles/:title

class Client < ActiveRecord::Base
  has_friendly_id :name
end