-At the part of the first level after the crash where a zombie throws a scientist through a window, run around the zombie and enter the lab to find a computer with an ultrasound image. That ultrasound image is of the unborn son of Randy Pitchford, the lead developer.
-Use the self-teleporting alternate fire mode of the Displacer right after getting that weapon while still on Xen. You will be transported back to the hazard course on Earth. Examine the bulletin board on the wall to see a picture developer Rob Heironimus.
-While in the "Boot Camp" level, activate the /noclip code. Pass through the floor then to find a hidden room with the message "DMM 1999", which is a reference to David Michael Mertz who developed this level.
-When starting the "Boot Camp" level, examine the names on the boxes beside the beds. They are the names of various developers.