Halo Reach Easter eggs

Fly a pelican!! (not glitched)
You will need two people on co-op for this cheat to work.
Go to the campaign mission "New Alexandria", the one where you have to fly the Falcon through the city. After about three objectives, you will get told to go the ONI HQ. Instead, go back to Club Errena, the building with red neon lights in the north-west part of the city. When you get there, go to the tall building to the the west (left if your facing the Club)
At the north-western corner to this building, there will be an alcove running all the way up the building. There is a small green switch at the top of this alcove that gets activated when you get sent to the ONI HQ. The easiest way I've found to hit this button is get another player to stand on top of the Falcon. When you hit the button, you need to go directly south, to find a building with a massive teardrop shaped hole at the top. If you've pressed the button and you go through the hole in a Falcon, then it'll be turned into a Pelican.
Unfortunately, Bungie have made the Pelican so that you can't a) fire the weapons, and b) you can't get out without the Pelican disappearing.
On the bright side however, if you can manage to hijack a Banshee in the level without dying, and you then follow the process above (note: you'll probably want to press the button with the Falcon BEFORE you hijack the Banshee, because it's almost impossible to press it on the back of a Banshee)and when you fly through the gap in the Banshee, it will transform into a Covenant Dropship instead of the Pelican!
Happy Hunting!