The Simpsons reference:
In the "High Tension" map, go the police station to find a few pink donut boxes
on a folding table in the garage bay. While looking at the boxes, press [Spot]
to shout "donuts spotted!".
Dead Space reference:
Play the "High Tension" map and go to the second floor of the shopping mall. One of the stores is named "Ishimura", which is a reference to the "USG Ishimura" mining spaceship in Dead Space.
Look for what appears to be a mild-mannered couch in the Dustbowl map on
Hotwire mode. Called the "The American Dream", players can in fact operate
it like a regular vehicle and it's one of the fastest to boot. The American
Dream can carry up to four players, and delivers appropriately amusing kill
feed messages should it run over anyone.