From time to time you might need to create an attribute which isn't linked to a particular product, but instead is linked to a category. A recent example (for me) was creating a block of overlay text to float above the category image.
Create a Category Attribute in Magento
But it's not as simple to create category attributes in Magento
as it is to create product attributes - but with a simple script it's not particularly difficult.
$installer = new Mage_Sales_Model_Mysql4_Setup;
$attribute = array(
'type' => 'text',
'label'=> 'Your attribute label text',
'input' => 'text',
'global' => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
'visible' => true,
'required' => false,
'user_defined' => true,
'default' => "",
'group' => "General Information"
$installer->addAttribute('catalog_category', 'ATTRIBUTECODE', $attribute);
It should go without saying that the ATTRIBUTECODE in the second to last line should be whatever you want your attribute's code to be
Save this file as a PHP file, upload it to the web root of your site, hit it in a browser and then look in the admin panel and you should see your new category attribute ready to use at the bottom of the General Information tab.