Has there ever been anything that properly classified the ghosts that are encountered by the Ghostbusters?

Tobin's Spirit Guide?

The most complete classification system was originally printed in the West End Games Ghostbusters: A Frightfully Cheerful Role Playing Game.

Considering how out of print the RPG is…the best place to find that would be over at Doc Fritz site:

http://ectozone.com/gbfl/terms.php

::edit::

A note of interest…West End Games also printed a Tobin Spirit Guide as an addendum to the rpg game

you know, i've always wondered the same thing myself. there's so many of them you kind of get confused after a while.

i think the closest they've come to something like that would be the recent video game