I just recently stumbled upon this particular site. It's pretty interesting in the sense that they offer a huge amount of old game manuals, reference crads etc. documentation for download as pretty good quality PDF files. They are a bit light on actual info about the games, but they do have some pretty old enteries there, from the 1970's to the 1990's. Furthermore, they don't offer game files, so it isn't an abandonware site.

The site itself isn't very navigation friendly IMO, but it is a pretty damn good effort in preserving more obscure and rare game documentation. They're particulary preserving adventure and RPG games.

http://www.mocagh.org/index.php

Well, I looked at some of the stuff they have, and I would guess that they haven't received a permission from Simon & Schuster to scan entire books as free PDFs.
And even if I try to be liberal with genre specifications, I don't understand how Pac-Man is in an adventure game museum.

Although as such it interesting that there actually were printed books on how to beat arcade games back in the day. Never really thought about that before, so if museums should be educational, I gotta give some credit for that, as I actually learned something.

Man....The stuff you find on the internet.

It's a fantastic source for documentation for old games - certainly the best I have seen. Before I start playing an old game, I always check there to see if it has anything I'm missing, or perhaps a better copy of what I do have.

So if you have not seen the site before, then it's well worth taking a look.