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.

George Pattichis

Simple CPT is a free WordPress plugin that lets you create custom post types and custom taxonomies (eg: categories, tags, etc.) directly from your admin dashboard without writing a single line code.
No more editing files manually. With Simple CPT you can create a new Custom Post Type in less than 1 minute.
This plugin is written using only native functions, included in WordPress core, so it does not in any way reduce the performance of your website and will not cause any compatibility problems. Simple CPT is completely free, it will save you time and it is compatible with almost all themes and plugins out there.
In just a few minutes you can adapt your WordPress site to any type of project in a professional and extremely efficient way, e.g. ecommerce, hotel, restaurant, events, portfolio, community websites etc.

Simple CPT

Simple CPT provides an easy to use interface for registering and managing custom post types and custom taxonomies.

WP Category Images vs Simple CPT