In Chapter 2:Freedom, there is a Deus Ex homage. The first line the black-marketeer inside the labor camp says is "You want to talk to El Ray? That's cool!" This is a direct quote from (and spoken with the same inflection as) a body guard for the Rook gang leader in the abandoned Brooklyn Bridge subway station.
In the map "Farm," find the tall tower with the yellow ladder. Once you are at the top, jump off and there will be a message that says "Press A to deploy parachute" and you can deploy a parachute and survive the fall
In the mission called Heartland you can find a QR code whcih you can read with a mobile phone. It points to this site, where you can check out wallpapers and videos: <a href="http://aug.me/SymB9t" target="_blank">http://aug.me/SymB9t</a>