<?php
function product_template() {
?>
    <li class="category-content-wrap">
        <center>
            <div class="category-content">
                <a href="<?php the_permalink();?>" rel="bookmark" title="<?php the_title_attribute(); ?>" style="text-decoration:none;">

                    <div class="category-content-image">
                        <?php the_post_thumbnail( "category-content-thumb" ) ;?>
                    </div>
                    <div class="category-content-name">
                        <h3>
                            <?php the_title ()?>
                        </h3>
                    </div>

                </a>
                <span class="additional">
                    <?php comments_popup_link( __( '0 comments'), __( '1 Comment'), __( '% Comments') ); ?>
                <?php edit_post_link( __( 'Edit'), '<span class="meta-sep">|</span> <span class="edit-link">', '</span>' ); ?>
                </span>
            </div>
        </center>
    </li>

<?php
}
$ctax = 'category';
$ptype = 'post';
$posts_per_page = 4;

$categories = get_categories( array ( 'taxonomy' => $ctax ) );
foreach ( $categories as $par_cat )
{
    if ( $par_cat->parent < 1 )
    {
        $par_catname = $par_cat->name;
        $par_catid = $par_cat->term_id;
        echo "<h2>$par_catname</h2>";
        query_posts( array( 'post_type' => $ptype, $ctax => $par_catname, 'posts_per_page' => $posts_per_page, 'order'=>'DESC', 'category__in'=>$par_catid ) );
        if ( have_posts() ) : while ( have_posts() ) : the_post();
            product_template();
        endwhile; endif; wp_reset_query();
    }

}
?>