Could also use get_pages for this, but…
<?php
//display all Pages that have a parent
$types[0] = 'page';
//$types[1] = 'post';
foreach ($types as $type) {
$args=array(
'post_type' => $type,
'post_status' => 'publish',
'showposts' => -1
);
$pages=get_posts($args);
if ($pages) {
echo '<p>Pages: </p> ';
foreach($pages as $post) {
setup_postdata($post);
if ($post->post_parent) { ?>
<p><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></p>
<?php
} // if ($post->post_parent
} // foreach($posts
} // if ($pages
} // foreach($types
?>
Related:
Stepping Into Template Tags
Stepping Into Templates
Template Hierarchy