Zelda and Doctor Who During the “Federation Day” campaign mission, after you enter the “CARANI” door, you can find a trophy in the shape of The Doctor's TARDIS with the words "Award for Largest Interior with Smallest Exterior", and next to it a Zelda rupee-shaped trophy with the words "for most bushes cut and pots smashed". There's also a trophy poking fun at the whole "world ending in 2012" event.
Modern Warfare During the mission "Atlas Falls" you will breach a recreational room. Search around to find an arcade machine called Call of Duty: Modern Warfare.
Teddy bear On the Flooded map, go to the center of the map and stand on the roof of a submerged bus. Look to the north to find a vent, then climb it and a teddy bear can be seen at the top, tucked between the vent and the wall.
Saving Private Ryan While playing the mission "All or Nothing" you come across a soldier about to be executed. If you kill every enemy around him you will be "Saving Pvt Ryan", a reference to the movie.
Star Wars Eventually (in the campaign) you will be tasked with sinking a ship with a Remote Controlled Torpedo. If you fail the first try, you will be told to "Aim for the thermal exhaust port", which is similar to what is told to Luke Skywalker and other pilots when setting out to destroy the first Death Star.
Platoon The father in the campaign is named Elias, just like Sgt. Elias out of the movie Platoon. Also, Rourke highly resembles Sgt. Barnes, with his dew rag and big scar running along his face.
Three Wise Monkeys In the perks menu under the Stealth category, the first three perks have icons with an X, representing no sound, no sight, and no hearing. This is similar to the Three Wise Monkeys, who are most famous for the proverb they are in which involves them "Seeing no evil, hearing no evil and speaking no evil".