Jam Taxonomy Image will help you have a nicer Category Page with banner for that category, and have a nice and powerful Taxonomy Widget.
This plugin will help you add a image ( thumbnail ) to Taxonomy like Category, Tag, Custom Taxonomy and display image via Widget, or function name 'get_taxonomy_image($term_id)' return URL image.
* Note: I do not add any CSS to Your theme header, and of course Image will have full size as you upload, so if you want to have a small thumbnail, you can add CSS or just upload a small image, if you want to display a banner for one category, you can upload a big picture or banner !
* This plugin include a nice Taxonomy Widget in Admin > Apearance > Widget, please check out !
No screenshots provided