Usage: http://jsfiddle.net/My9qq/1/

getScriptOnce.js

(function($) {

var $scripts = [];
$.getScriptOnce = function(url, success){

	if(url instanceof Array && url.length==1)
	{
		url = url[0];
	}
	else if(url instanceof Array)
	{
		var first = url.shift();
		$.getScriptOnce(first, function(){
			$.getScriptOnce(url, success);
		});
		return;
	}
	
	url = url + $.getScriptOnce.url_sufix;

	if(typeof $scripts[url] == 'undefined')
	{
		$scripts[url] = {status: 0, callback: []};
		
		if($.isFunction(success))
		{
			$scripts[url].callback.push(success);
		}
		
		$.getScript(url, function(xhr, status){
			$scripts[url].status = 1;
			$.each($scripts[url].callback, function(i, callback){
				callback(xhr, status);
			});
			$scripts[url].callback = [];
		});
	}
	else if($scripts[url].status==0 && $.isFunction(success))
	{
		$scripts[url].callback.push(success);
	}
	else if($.isFunction(success))
	{
		success();
	}
};
$.getScriptOnce.url_sufix = "";

})(jQuery);