Add ?loggedoutview=1 to the end of any URL to see what it looks like for logged out users.

logged-out-view.php

<?php
/*
Plugin Name: Logged Out View
Plugin URI: http://www.strangerstudios.com/wp/logged-out-view/
Description: Add ?loggedoutview=1 to the end of any URL to see what it looks like for logged out users.
Author: Stranger Studios
Version: .1
Author URI: http://www.strangerstudios.com
*/

function lov_set_current_user()
{
	if(!empty($_REQUEST['loggedoutview']))
	{
		global $current_user;
		if(!empty($current_user) && $current_user->ID > 0)
			wp_set_current_user( 0 );				
	}
}
add_action('set_current_user', 'lov_set_current_user');

Possible improvement:
(1) persisting the ?loggedoutview parameter (hint: use home_url and site_url hooks and add query arg())