wordpress show similar posts
<ul class="some-class">
<?php
$related = get_posts( array( 'category__in' => wp_get_post_categories($post->ID), 'numberposts' => 3, 'post__not_in' => array($post->ID) ) );
if( $related ) foreach( $related as $post ) {
setup_postdata($post); ?>
<li>
<a href="<?php the_permalink() ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a>
<div><?php the_excerpt();?></div>
</li>
<?php }
wp_reset_postdata(); ?>
</ul>