dmikam

This simple plugin permits you to upload images to categories, tags and custom taxonomies just like to posts. 
This feature is very useful when you want to show unique image in header tor every category or even some slideshow of images. 
Also you can show a list of categories/subcategories with a little thumbnail am much more.
By the way, this plugin just uses wordpress native functionality – no aditional tables and nothing like that. 
Also it uses wordpress images so all sizes are generated automatically (custom sizes included).

WP Category Images

Simple plugin that permits to images to Categories, Tags and Custom Taxonomies.

prettyboymp

CMS Press opens up the ability to create and manage custom content types and taxonomies for your WordPress site. 
It adds the flexibility to have more than just posts and pages for content by allowing the user to register their 
own post_types that can use their separate theming from the post and page template along with its own permalink structure.
Along with custom post_types, CMS Press gives users the ability to register their own taxonomies. With the addition of 
custom taxonomies, a user can tag or categorize content separate from the default tags and categories.

CMS Press

Adds ability to create custom content types (post_types) and taxonomies to your WordPress installation.

WP Category Images vs CMS Press