The core helper ( Mage::helper('core') ) has a method in it which you can use to format the currency.
<?php echo Mage::helper('core')->currency($_product->getPrice()) ?>
As an alternative, you are able to get the currency symbol as a stand alone option as well.
$symbol = Mage::app()->getLocale()->currency(Mage::app()->getStore()->getCurrentCurrencyCode())->getSymbol();
echo $symbol;
My recommendation is to use the first option (the core helper) since it is the primary purpose of using helpers.
References Magento Core Helper Documentation