<?php
if($_product->getTypeId() == "configurable") {
    $ids = $_product->getTypeInstance()->getUsedProductIds();
?>
<ul>
    <?php
    foreach ($ids as $id) {
        $simpleproduct = Mage::getModel('catalog/product')
              ->load($id);
    ?>
        <li>
            <?php
            echo $simpleproduct->getName() . " - " . 
     (int)Mage::getModel('cataloginventory/stock_item')
             ->loadByProduct($simpleproduct)->getQty();
            ?>
        </li>               
    <?php
    }
    ?>
</ul>
<?php
}
?>