Doom 3 Easter Egg - In-Game Credits

The entrance to this easter egg is located on the map Excavation Site (final level) right before you enter the halls of CyberDemon.
In the lower dungeons right before you reach the place where the wall bursts open and the in-game cinematic of you finding the final boss boots up, walk left.
This will take you to a dead end but if you crouch and face the wall of the actual dead end, right above the floor under a few protruding bricks, you will find the id-logo etched in the stone wall. Place your cross-hair over it and it will give off the regular blip-sound you get when you use a computer. Now click the logo and it along with the brick it is etched on will sink into the wall with a scratching noise. Now a new path to your left will open, leading you into a chamber filled with an eerie red light and a huge horned skull on the wall in the back. Below the skull is a bloody pentagram with a PDA positioned in the middle. Download the data from the PDA into your own and see what you got. You will find data from the PDA of "iD-Software" and it is filled with e-mails from everyone involved in the Doom III-project thanking their loved ones, their fans and giving their general thoughts on the projects.

Spooky, yet pleasantly refreshing to see right before the final showdown!