There are various election signs that can be found in the game that read "Richard Grimes for Sheriff". This is a reference to the main character of The Walking Dead TV series, sheriff Rick Grimes.
Xbox 360 Slim consoles, along with an Xbox 360 Controller, can be found within a number of houses throughout the game.
In an office, you can see 4 posters for the American cities "Wichita", "Tallahassee", "Little Rock" and "Columbus". This may be a reference to the film "Zombieland", whom the four main characters in the movie are named after.
Behind a house there is a garden that has sunflowers and lawn mowers. This is a reference to Plants VS. Zombies. Also, there is one zombie that was killed by a lawnmower.