http://www.snescentral.com/unreleased.php
I'm making up a master list of titles for the SNES that are known to be unreleased. The games on this list have at least some level of verification that they did truly exist in some form, and I would rather not put on games that are purely speculative (i.e. Super Mario FX). I'm up to 165 titles on that list, and certainly there should be more. I'm always looking for binaries of these games, so if you have a binary of an unreleased game that I have listed as "no", please let me know. If you have a title that is missing, let me know the source (or better yet, make a picture/scan of it), and I will add it to the master list.