Arno Welzel

This widget displays top level categories in multiple columns.
After installation, just add the widget to desired sidebar or footer and optionally enter a custom title and the number of columns to be displayed.
By default two columns are used, but you can set any number of columns you like in the backend.
Also see details at <a href="http://arnowelzel.de/wp/en/projects/wordpress/multicolumn-category-widget" rel="nofollow ugc">http://arnowelzel.de/wp/en/projects/wordpress/multicolumn-category-widget</a>.

Multicolumn Category Widget

This widget displays top level categories in multiple columns.

Dominik Schwind

Enables a widget with the category description. This is useful if the theme you are using is not showing 
this information.
Works on tags and other taxonomies as well.

Category Description Widget

Enables a widget with the category description.

Multicolumn Category Widget vs Category Description Widget