gistfile1.php

<?php

function menu_children_alphabetical_reorder($plid) {
  if ($children = db_query("SELECT mlid, link_title FROM {menu_links} WHERE plid = :plid", array(':plid' => $mlid))->fetchAllAssoc()) {
    natcasesort($children);
    $weight = 0;
    foreach (array_keys($children) as $mlid) {
      db_update('menu_links')
        ->fields(array('weight' => $weight++))
        ->condition('mlid' => $mlid)
        ->execute();
    }
  }
}

function menu_children_alphabetical_menu_link_insert($link) {
  if ($link['plid'] == 500) {
    menu_children_alphabetical_reorder($link['plid']);
  }
}

function menu_children_alphabetical_menu_link_update($link) {
  if ($link['plid'] == 500) {
    menu_children_alphabetical_reorder($link['plid']);
  }
}