<?php

$result = mysql_query("

  SELECT

    *

  FROM

    some_table

  ORDER BY

    company,

    category,

    brand

") or trigger_error('Query failed in '. __FILE__ .' on line '. __LINE__ .'. '. mysql_error(), E_USER_ERROR);

if (mysql_num_rows($result)) {

  $companies = array();

  while ($row = mysql_fetch_assoc($result)) {

    $companies[$row['company']][$row['category']][] = $row['brand'];

  }

​

  foreach ($companies AS $company => $categories) {

    echo '<h2>'. htmlentities($company, ENT_COMPAT, 'UTF-8') .'</h2>';

    echo '<ul>';

    foreach ($categories AS $category => $brands) {

      echo '<li>'. htmlentities($category, ENT_COMPAT, 'UTF-8');

      foreach ($brands AS $brand) {

        echo '<br><em>'. htmlentities($brand, ENT_COMPAT, 'UTF-8') .'</em>';

      }

      echo '<br>&nbsp;</li>';

    }

    echo '</ul>';

  }

}