Other Easter Eggs

Dead Island Easter Egg
Proceed through the main story missions until you can leave the simulator. When you leave the simulator, go over to Keith David, and keep talking to him until he mentions the Dead Island game. One of Keith David's dialogue lines is "I was twelve hours into Dead Island, now I'll never finish it. I can't forgive Zinyak for that."

Mass Effect 3 Easter Eggs
In addition to the "romance skipping straight to sex" as a jab at Mass Effect 3's romance system, during the Zin attack on the White House, the Reaper laser sound effect can be heard.

Metal Gear Solid series Easter Eggs
You are supposed to sneak through one of the missions by shooting light bulbs, and then the guards under them. When the light bulbs are shot, "WTF" appears over the guards heads, like the exclamation point in the Metal Gear Solid series. You can also sneak under a box and fight an evil twin, which both occurred in Metal Gear Solid.

Minecraft Easter Egg
During a Security Deletion mission, the selected target you are required to kill is a Minecraft character.

Saints Row series Easter Eggs
The simulation "Leave It To The Saints" is a parody of Leave It To Beaver. One of the things the mother says is "Someone named Dex was here asking for you, but I didn't recognize him so I sent him away." This is a reference to Dex, a former member of the Saints who did security for Ultor, and then turned terrorist in the Saints Row 2 DLC. He was supposed to appear in Saints Row: The Third, but was left out because "Newcomers to the series wouldn't recognize the character and they didn't want to alienate them."
Kinzi says that Keith David's voice is similar to Julius. Keith David provided the voice for himself and Julius Little.

Space Invaders Easter Egg
At the beginning of the game when the president uses the gun turret to destroy alien ships, the alien ships will line up just like in the Space Invaders game.

Streets Of Rage Easter Egg
During a mission, you play a side-scroller called "Saints Of Rage".

Terminator Easter Egg
During the "Ghost In The Machine" main story mission, you will encounter the "murder bots" (you will also encounter this enemy throughout the game). They look exactly like the Terminator, and their weapons sound the same as the Terminator's weapons.

The Hitchhikers Guide To The Galaxy Easter Egg
The "Don't Panic" achievement is earned when the earth is blown up by Zinyak. It is a reference to the words "Don't Panic" written on The Hitchhikers Guide To The Galaxy's book cover, in which Earth is blown up by an alien race.