Is it possible to display a clickable, self-updating list of subsites on the top-level site?
Also, is it possible to further sort the list according to the subsite category?
if it is, how can you place subsites into categories?
One idea would be that you can use the tree view in the top level site to list Sites with their appropriate subsites, lists, and libraries, although they cannot be put into categories.
Site Actions -> Site Settings -> Tree View -> Enable