As shown elsewhere, you can add an attribute to the category entity in Magento. If the attribute is of type select, getting the text value of an option is a bit of a pain:
$category = Mage::getModel(‘catalog/category’)->load(10);
$attribute = Mage::getSingleton('eav/config')->getAttribute('catalog_category', 'myattribute_code');
$text = $attribute->getSource()->getOptionText($category->getMyattributeCode());