This cool little theme code snippet allows the wordpress navigation to link to a page outside of wordpress. It takes advantage of custom fields for pages. 
Just place this code at the top of your themes header.php file
<?php
/*
Copyright (c) 2009 < Nate Nuzum >
Use under terms of MIT license
*/
global $post;
$redirect = get_post_meta($post->ID, 'redirect', true);
if ($redirect)
wp_redirect($redirect);
?>
Then create a page with the name having the link text you want to appear in the navigation add a custom field to the page called redirect and place the link url into the value field.
