WordPress 2.8 and up allow for reasonably simple custom taxonomies, this plugin makes it even simpler, removing the need for you to write any code.
This plugin allows you to add taxonomies just by giving them a name in the backend. It then creates the taxonomy for you, takes care of the URL rewrites, provides a widget you can use to display a "taxonomy cloud" or a list of all the stuff in there, and it allows you to show the taxonomy contents at the end of posts and excerpts as well.
To boot, it comes with a set of template tags for those who don't mind adapting their own theme.
For full info go the Simple Taxonomies page.