This plugin implements the metadata infrastructure for taxonomy terms, so you can add custom metadata (by key) to tags, categories, and other taxonomies.
Query multiple taxonomies.
Create many-to-many connections between posts of all kinds.
I’ve been using the new [Twenty-Ten](http://wordpress.org/extend/themes/twentyten) theme for WordPress on my personal website; it’s great out of the box, but I wanted to display my custom post types and taxonomies in the same format as it uses for categories and tags. The function is broken into two parts: `ucc_get_terms()` returns a multidimensional array of the post’s taxonomy name(s) and each taxonomy’s term links; `ucc_get_terms_list()` gets the taxonomy information and formats the array for display in the template.
The WordPress Categories Widget currently only handles the `category` taxonomy. I’ve modified it to allow the user to select a taxonomy, and tied in the Tag Cloud Widget code to give the user the choice of display formats: list, dropdown, and cloud. Multiple instances are possible, providing the user with an easy method for displaying links to user-built taxonomy terms.