Please add this in your phtml file where you want to add :
<div class="add-to-cart">
<div class="qty-view">
<?php if(!$_product->isGrouped()): ?>
<label for="qty"><?php echo $this->__('Qty:') ?></label>
<input type="text" name="qty" id="qty" maxlength="12" value="<?php echo $this->getProductDefaultQty() * 1 ?>" title="<?php echo $this->__('Qty') ?>" class="input-text qty validate-greater-than-zero-qty validate-digits" />
<?php endif; ?>
</div>
<button type="button" class="button btn-cart" onclick="productAddToCartForm.submit(this)"><span><span><?php echo $buttonTitle ?></span></span></button>
<button type="button" title="Buy Now" class="button btn-cart" onclick="setcheckoutLocation('<?php echo $this->getAddToCartUrl($_product) ?>')"><span><span>Buy Now</span></span></button>
<?php echo $this->getChildHtml('', true, true) ?>
</div>
and must be added this script for Buy Now button :
<script type="text/javascript">
function setcheckoutLocation(location)
{
showLoadingAnimation();
jQuery.ajax({
type:"GET",
url:location,
success:function(data){
window.location.href = "<?php echo Mage::helper('checkout/url')->getCheckoutUrl(); ?>";
}
});
}
</script>