The ZYX Term Meta plugin/framework adds a term metadata table and puts it to good use with a zillion features, from term alias to custom templates, multiple parents for child terms, HTML HEAD metadata, term thumbnails/featured images, a much improved user interface and much, much more: even a theme. You'll be able to choose which features you need, and deactivate those you don't need.
Please note: Some of the features of this plugin are intended to use, or best used, with categories. Some of the features may be tweaked to work with other taxonomies, but actually this is not needed thanks to the term group and link to page features, which allows all the features for taxonomies (like meta boxes, permalinks and templates), and even more: see the description of term groups for a (somewhat) full list of features.
This "special category support" is due mainly to two reasons: One, the object $wp_query has a superb support for categories. It allows for many combinations, while taxonomies were requested just with a rewrite (which meant that you could not ask for ingredient="bread" AND process="baking", you just could query where taxonomy=ingredient AND term=bread , or taxonomy=process. And, also, at the start of development of this plugin, there was no real support for hierarchical taxonomies other than category, so useful things like the multiple parentage where anyway limited to categories only.