gistfile1.js

//######### How to send authenticity_token automatically with every Ajax.Request.
//######### This will be obsolete in Rails 3 (as Yehuda mentiones here : https://rails.lighthouseapp.com/projects/8994/tickets/2696-prototypehelper-no-auth-token-param-for-get-requests#ticket-2696-2)

//######### Put this in your application.js
// Monkeypatches Ajax.Base to include authenticity_token parameter unless its already there
(function() {
	function insert_auth_token (options) {
		var o = options || {};
		if (typeof(o.parameters) == "String" && !o.parameters.include("authenticity_token")) {
			o.parameters = o.parameters + "&authenticity_token="+AUTH_TOKEN; 
		} else {
			o = Object.extend({ parameters: { authenticity_token: AUTH_TOKEN} }, o);
		}
		return o;
	}	
	// Prototype's Function#wrap something like alias_method_chain
	Ajax.Base.prototype.initialize = Ajax.Base.prototype.initialize.wrap(
		function(proceed, options) { 
      return proceed(insert_auth_token(options)); 
    }
  );
})();

//######### Put this in your Layout
<%= javascript_tag "var AUTH_TOKEN = #{form_authenticity_token.inspect};" if protect_against_forgery? %>

//######### If you don't have to use Protoype, here's how to do this with JQuery http://henrik.nyh.se/2008/05/rails-authenticity-token-with-jquery