I'm currently a co-admin of The Cutting Room Floor Wiki (see this link), where we document prototypes, revision/regional differences, obscure easter eggs (dev messages exposed through hex editing also count), and, of course, unused content tucked away in video games.
I'm curious if anyone's found anything that didn't go used in a Mac game. The most luck I've had so far is finding developer messages easily exposed with ResEdit.
At the moment, I'm converting the stuff from bungie.org over to the wiki.
If anyone wants to edit the wiki, make sure to check the help page.