microkid + yarpp

if ( function_exists('MRP_show_related_posts')) {
    echo "<hr />\n";
    $related_posts = MRP_get_related_posts( $post->ID, true );
    if ($related_posts) {
        MRP_show_related_posts();
    } else if ( function_exists('yarpp_init')) {
        related_posts();
    }
} else if ( function_exists('yarpp_init')) {
    echo "<hr />\n";
    related_posts();
}