Ok - this isn't the most sophisticated of plugin, but it is my first attempt :)
catList 1.0: http://memetic-selection.no-ip.info/?p=116
catList is a plugin to generate a fully customizable, formatted list of a blog’s categories along with their descriptions - something not possible with the existing template tags. Completely option driven, CSS styled, and as flexible as I could make it. Have a look.
Feedback, bugs, comments welcome.