Plugin that lets you create descriptions for individual categories

I’m looking for a plugin that allows you to create/assign individual descriptions for/to individual categories that appears in the sidebar, like the common ‘About the Author’ paragraph often found at the top of the sidebar.

I know about the “You are currently browsing archives…” text that comes as standard in the default theme but I’d like to have this function to work for individual categories so that I could have a description of the category the person is browsing appear in the sidebar.

I think this would improve usability, especially when people arrive at a post page, rather than the home page, when visiting the site for the first time.

Does anyone know of a plugin that achieves this functionality? I couldn’t find one by searching the web or the forum.