I've recently discovered The Cutting Room Floor, a comprehensive wiki on unused/beta/debug stuff in games. Since I'm really interested in these sort of things, I'm writing their Megaman Battle Network articles since I know the most about those things when it comes to the MMBN series. I'll be starting with the first game and go in order. I know there will be plenty to go over so remember to check out the articles soon.
Update: I've finished writing the MMBN1 page. If I can discover more things, I will add them.