Eu no mais-sites utitlizo isto
no php do post
<h4>Conteúdo Relacionado</h4>
<?php $container = ar_related('4','thumbs'); echo $container['related']; $post = $container['post']; ?>
</div>
<?php while (have_posts()) : the_post(); ?>
e no funcionts do tema
//Related post by category
function ar_related($limit=NULL,$type=NULL){
global $post;
$current_post = $post;
$current_post_id = $post->ID;
if(!$limit){
$limit = 4;
}
$upper_limit = $limit * 2;
$i = 0;
foreach((get_the_category($post->ID)) as $category) {
$related_cats[$i] = $category->cat_ID;
$i++;
}
if($i > 1){
shuffle($related_cats);
}
$related_cats = implode(',',$related_cats);
if($related_cats){
$related_query = new WP_Query("cat=$related_cats&showposts=$upper_limit");
$i =0;
while ($related_query->have_posts()) :
$related_query->the_post();
if($post->ID != $current_post_id){
if($type == "thumbs"){
if(get_post_meta($post->ID, "post-image", $single = true)){
$related_posts[$i] = '<a href="'.get_permalink().'"><img src="'.get_bloginfo('template_url').'/scripts/timthumb.php?src='.get_post_meta($post->ID, "post-image", $single = true).'&h=115&w=115&zc=1" style="float:left; width:115px; height:115px; margin:5px 12px; padding:2px; border:1px solid #e7e7e7;" alt="'.get_the_title().' - Thumbnail" title="'.get_the_title().' - Thumbnail"></a>';
}
}
else{
$related_posts[$i] = '<li><a href="'.get_permalink().'">'.get_the_title().'</a></li>';
}
$i++;
}
endwhile;
if($i > 1){
shuffle($related_posts);
}
$i = 0;
while($i < $limit){
$output .= $related_posts[$i];
$i++;
}
if(count($related_posts) <= 1){
$output = "<span style=\"color:#555; font-style:italic;\">This is the first post in this category. <a href=\"".get_bloginfo('rss2_url')."\">Subscribe to the RSS feed</a> to find out when more content is added.</span>";
}
else{
$output.='<div class="clear"></div>';
}
}
$post = $current_post;
$container['related'] = $output;
$container['post'] = $post ;
return $container;
}