I have found 2 Easter eggs in Reach so far, and i am looking for more. The second one is kinda dumb, but it's still an Easter Egg.

1. On the Campaign level "New Alexandria" There is a part where you get to a place that looks like the level "Reflection" on multiplayer. If you go where the top of the elevator is(Think of this as just getting off of the elevator) and turn left, there will be a spot where there is a drop. Right in front of the drop, there is a marine with a pistol to his head saying he'll kill himself because he doesn't want to turn into one of them. He's not really gonna kill himself, but it's still fun to watch him complain and act like he's really gonna do it. The spot may be hard to find, because there's no elevator on New Alexandria, but if you know about the ramps that lead up to that same spot, you'll find him.

2. On the final level (I forgot the name) of campaign, right before you get on the giant anti-air cannon, there is a bunch of dead Elites lying on the ground. If you step on one, you notice that you step on top of them, and not through them, and if you punch one, the shield depletes, as if it were alive. Like I said above, it's a dumb Easter egg, but still an Easter egg.