Some of the goodies are impossible to see unless you can actually move around the map without the normal constraints of the game.  To do this you'll have to bring down the console via the tilde key and type "/devmap mapname".  Map name being q3dm19 or whatever.   Once the map has loaded, bring down the console once again and type "/noclip".  This will allow you to move about the map freely.   Remember the quotation marks are not necessary.  Have fun!!

Map: Q3DM11		You can find this one by going to the transporter with the shotgun spawning directly in front.  If you turn around and face away from the shotgun towards the wall you'll enter a secret chamber that gives health and displays the death fish!!
Map: Q3DM15		If you go to the room below the outside area that leads to the jump pad where the rocket launcher spawns, you will find a head.  It looks like John Carmack?
Map: Q3DM16		You will find this underneath the bottom of the map dead center.  It's the main character from the "User Friendly" comic strip featured on Blues News.
Map: Q3DM19		This easter egg is also found underneath the main platform dead center.  Same guy from "User Friendly."
Map: Q3DM19		Go to the moving platform that has the antennea and look at it's backside.  You'll see a freaky face there.