Plugin for custom page for each category

I have about 20 categories. Instead of having each category being little more than a title tag, I’d like to be able to have a page assigned to the category that I can have unique text and layout for that category. For example, if it is a cars category, I’d have text about the cars section, probably put up a sponsor’s banner or two, and then have latest articles appearing below it. It’s practically the same that you can do with a static page assigned to a front page and a theme allows you to choose widgets to assign how posts should appear.

So far I’ve been managing this manually with coding that puts in a different text file before every layout for each category, which is a huge pain and unwieldy. I was wondering whether anyone has created such a plugin.