rails-assets-cdn

# serve all assets from CDN  server
config.action_controller.asset_host = 'http://cdn.mydomain.com'

#or if your files in a folder on CDN server
config.action_controller.asset_host = 'http://cdn.mydomain.com/myfolder'


# serve only images
config.action_controller.asset_host = Proc.new { |source|
    if source =~ /\b(.png|.jpg|.gif)\b/i
      "http://cdn.mydomain.com"
    end
  }