http://www.h-o.nl/blog/display-special-priced-products-on-homepage-magento/

addAttributeToFilter.php

$dateToday = date('m/d/y');
$tomorrow = mktime(0, 0, 0, date('m'), date('d')+1, date('y'));
$dateTomorrow = date('m/d/y', $tomorrow);

$this->_productCollection
->addAttributeToFilter('special_from_date', array('date' => true, 'to' => $dateToday))
->addAttributeToFilter('special_to_date', array('or'=> array(
	0 => array('date' => true, 'from' => $dateTomorrow),
	1 => array('is' => new Zend_Db_Expr('null')))
), 'left');

addAttributeToFilter2.php

$this->_productCollection
->addAttributeToFilter('special_from_date', array('date' => true, 'to' => $dateToday))
->addAttributeToFilter('special_to_date', array('date' => true, 'from' => $dateTomorrow));

getProductCollection.php

$this->_productCollection = $layer->getProductCollection();

product.featured.xml

<reference name="content">
	<block type="catalog/product_featured" name="product.featured" template="catalog/product/featured.phtml">	
	<action method="setCategoryId"><categoryid>300</categoryid></action>	
		<block type="catalog/product_list_toolbar" name="product_featured_toolbar" template="catalog/product/list/toolbar.phtml">
		    <action method="addPagerLimit"><mode>list</mode><limit>5</limit></action>
		</block>
	<action method="setToolbarBlockName"><name>product_featured_toolbar</name></action>
	</block>
</reference>

Product_List.php

class Mage_Catalog_Block_Product_List extends Mage_Catalog_Block_Product_Abstract

product_list.xml

<reference name="content">
	<block type="catalog/product_specials" name="product_list" template="catalog/product/list.phtml">
	
	<action method="setCategoryId"><categoryid>2</categoryid></action>
        <action method="addColumnCountLayoutDepend"><layout>three_columns</layout><count>3</count></action>
	<action method="setToolbarBlockName"><name>product_list_toolbar</name></action>
	
	<block type="catalog/product_list_toolbar" name="product_list_toolbar" template="catalog/product/list/toolbar.phtml">
		<block type="page/html_pager" name="product_list_toolbar_pager">             
	</block>
	</block>
</block></reference>

Product_Specials.php

class Mage_Catalog_Block_Product_Specials extends Mage_Catalog_Block_Product_Abstract