Custom Taxonomies provides a full administrative interface for creating and using taxonomies beyond the standard Tags and Categories.
WordPress provides a lot of functionality geared towards the use of generic "taxonomies", such as Tags and Categories, but no way to manage the taxonomies themselves. This plugin allows you to:
Note: 2.6/2.5 support is still in development, it's not themed properly and isn't guarenteed to work properly. Please submit bug reports here.