1. Your in one. There are a lot of prototypes documented right here. Information can be found in threads, in the database, and a few well written ezine articles.
2.
http://assemblergames.com/index.h... is another forum so digging is going to be required. Their tag line is home of the obscure. I have found lots of helpful information there. Sadly they are currently down.
3.
http://hiddenpalace.org/... This is a wiki dedicated to cataloging prototype games for all systems.
4.
http://www.nintendoplayer.com/&nb... is a person's personal website that documents Nintendo prototypes and some random 80's culture. His features often include interviews with staff or developers. The operator, Mike, has slowed down as his real life responsibilities have grown. It is near and dear to my heart as it is what got me into prototypes to begin with.
5.
https://tcrf.net/The_Cutting_Room... is a website dedicated to unused sprites, code, etc. from video games. Most of the information there is from retail games, but they also have prototype info.
6.
http://bootgod.dyndns.org:7777/&n... is probably the single most useful site when checking out NES prototypes. It is a database of what NES games look like inside and out. They have a few prototype profiles too.
7.
http://lostlevels.org/... This website is dedicated to unreleased games. It is run by NA member TheRedEye.
8.
http://www.nesworld.com/nesprotot... website dedicated to NES. It has a good NES prototype photo database.