This one is very simple. For those of you that want to automatically include it in your themes, you can query by comment count using get_posts and running a foreach loop to get the contents. Very simple procedure.

Code below will output the most popular post by comment count.

[php]
<? $args = array(‘posts_per_page’ => 5, ‘orderby’ => ‘comment_count’);
global $post;
$popular = get_posts($args);
foreach($popular as $post) {
setup_postdata($post); ?>

<a href="<?php the_permalink(); ?>"><?php the_title();?></a>

<?php endforeach;?>
[/php]

Give it a try on your template.