Show related posts without a plugin

Installing the code below will make your WordPress site display related posts based on the current post tag(s). You need to place it inside single.php, or simply anywhere you want to show the related posts.

<?php
    $tags = wp_get_post_tags($post->ID);
    if ($tags) {
        $tag_ids = array();
        foreach($tags as $individual_tag) $tag_ids[] = $individual_tag->term_id;
        $args=array(
        'tag__in' => $tag_ids,
        'post__not_in' => array($post->ID),
        'showposts'=>5, // Number of related posts that will be shown.
        'caller_get_posts'=>1
        );
    $my_query = new wp_query($args);
        if( $my_query->have_posts() ) {
            echo '<h3>Related Posts</h3><ul>';
            while ($my_query->have_posts()) {
                $my_query->the_post();
                ?>
                <li><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></li>
            <?php
            }
            echo '</ul>';
        }
    }
?>