Widget/sidebar for each category?

Hi
Is there such a plugin available:

I’d like the posts in each category to show it’s own sidebar – or even better: To have one widget to show up on the posts of each category.

I’m converting a site about Italy, and for each region I’d like the top of the sidebar to show info, links etc which are relevant for just that region.
Eg, on the Toscana page I would like it to show links to local places, photo galleries etc which are not relevant on the Sicilia posts – have a look at the right side here.
So – I don’t need a widget that displays categories, but a plugin that assigns one unique widget in the sidebar of each category’s posts.

I’ve tried to achieve it using the html templates and the Widget changer. The widget changer comes closest, but since it can only be used on posts (and pages), and not on categories, it has to be inserted and even edited in the posts one by one. (I’d even have to format/prepare the contents in an html editor, Dreamweaver or the like.)

Such a plugin would save me lots of work, so I’m grateful for any suggestions.

Thanks,
Kjetil