Add Payment Method Custom column in admin > sales > order

1.)  Copy /app/code/core/Mage/Adminhtml/Block/Sales/Order/Grid.php to
 /app/code/local/Mage/Adminhtml/Block/Sales/Order/Grid.php. 

And replace with this function.

protected function _prepareCollection()
    {
         $collection = Mage::getResourceModel($this->_getCollectionClass());
         $collection->join(array('payment'=>'sales/order_payment'),'main_table.entity_id=parent_id','method');
         $this->setCollection($collection);
         return Mage_Adminhtml_Block_Widget_Grid::_prepareCollection();
         // end here //
    }

2.)  Search the function _prepareColumns() and add below code in this function
 

$payments = Mage::getSingleton('payment/config')->getActiveMethods();

        $methods = array();
        foreach ($payments as $paymentCode=>$paymentModel)
        {
                $paymentTitle = Mage::getStoreConfig('payment/'.$paymentCode.'/title');
                $methods[$paymentCode] = $paymentTitle;
        }

        $this->addColumn('method', array(
                'header' => Mage::helper('sales')->__('Payment Method'),
                        'index' => 'method',
                        'filter_index' => 'payment.method',
                        'type'  => 'options',
                        'width' => '70px',
                        'options' => $methods,
                ));
        // End here