WordPress.org

Author: Brahim Machkouri

Assigns icons to categories with WordPress 2.3 or higher. This wonderful plugin :

• displays one or more icons in front of your post title or wherever you want
• displays icons in the sidebar, with or without the category name, with or without the help of the widget
• includes a widget. You can : use multiple Category Icons widgets (for WordPress 2.5 and higher), include or exclude some categories, display only icons (i.e. without the category name)...
• you can make rollover with the icons in the sidebar if you follow this tutorial
• is able to display category icons in your RSS
• will either show you where to place the little code needed in your themes, or patch them automatically
• generates pure html code of the img tag, so it gives you the freedom of doing what you want to with the icons (customizing via CSS or not)
• generates valid XHTML (and Strict XHTML)
• can prioritize the icons display (by Oliver Weichhold)
• is translated in 20 languages (all the .po files are included, in case you want to update your language) : Arabic (ar) by Ahmad Bekdash, Belarusian (be_BY) by Fat Cower, Brazilian Portuguese (pt_BR) : 3 versions (!) by Pedro Germani, Helder Vieira & Rodrigo Vieira Alves, Bulgarian (bg_BG) by Kalin Dimitrov,
  Chinese (zh_CN) by ?, Chinese Taïwan (zh_TW) by Hugo Chen, Czech (cs_CZ) by Spazi, Danish (da_DK) by Henrik Schack, Dutch (nl_NL) by Vincent Sparreboom, French (fr_FR) by Brahim Machkouri, German (de_DE) by Kristian Bollnow, Italian (it_IT) by Gianni Diurno, Japanese (ja) by Tenderfeel, Polish (pl_PL) by Shlizer, Russian (ru_RU) by Dimox, Slovak (sk) by Samuel Kroslak, Spanish (es_ES) by TechnopodMan, Swedish (sv_SE) by P-C, Turkish (tr_TR) by Selim Basak, Ukrainian (uk_UA) by Andrew Senyshyn
• is compatible with these powerful plugins : My Category Order, qTranslate, Recent Posts, SEO Friendly Images, Similar Posts
• is compatible with WordPress MU

You can have a look to the changelog.

Or maybe you were looking for Category Icons Module ?