<?php

// Special pages
$frontpage_id = get_option( 'page_on_front' );
$blog_id = get_option( 'page_for_posts' );

// Page templates
$about_templates = get_pages(array(
	'meta_key' => '_wp_page_template',
	'meta_value' => 'page-about.php'
));
$about_id = $about_templates[0]->ID;

?>

<!-- Usage: -->
<a href="<?php echo get_permalink($about_id); ?>">About Us</a>