To make my admin Sales/Orders grid better added column to the grid:
[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/BmXUD.png


and as on the picture above it shows order delivery method but ...
how to create "delivery method" dropdown list to make it easier to use?
So far I tried to add a class:

    public function getCarrierList()
	{
		$shippingMethods = Mage::getSingleton('shipping/config')->getActiveCarriers();	
		$methods = array();
		foreach($shippingMethods as $method)
		{
				$methods[$method['value']] = $methods[$method['label']];
		}
		return $methods;
	}

and added to the column definition:

    
		$this->addColumn('shipping_method', array(
			'header' => Mage::helper('sales')->__('Shipping Method'),
			'index' => 'shipping_description',
			'type'=> 'options',
			'filter_index' => 'shipping_method',
			'options' => $this->getCarrierList(),
		));
		
but then my column stays empty and drop-down is also empty.