Category Meta plugin by Eric Le Bail and Tom Ransom adds meta data to the wordpress categories and terms. It Creates a wp-termsmeta table to store the entered meta. It adds input fields to the category and other term administration interface to enter the meta values. It provides functions to retrive / create / update / delete the category and terms meta. It can be used to add meta to custom taxonomies (terms).
This plugin has been tested with WP2.8.6 and WPmu2.8.6 and WP3.0
Download and info: http://wordpress.org/extend/plugins/wp-category-meta/