Halo: Combat Evolved Cheats

Apparently, the guys at Microsoft/Bungie/Gearbox have a good sense of humor, and they like Green Day.

On the title screen, click Multiplayer, and put your mouse pointer over the "Edit Gametypes" option. Look at the specs that are being pointed out on Master Chief's suit.

-The one pointing at his chest says "All your base are belong to us," which we all know came from Zero Wing's horrible translation.
-Another one pointing at his thigh pad says "Sometimes I give myself the creeps sometimes my mind plays tricks on me," which are lyrics from Basket Case by Green Day.

Warning! This cheat may require you to start the level again.
On the last level(The Maw) when Echo 419 gets shot down, go down aways until you see a tunnel on your right. Get out of the warthog and go through the tunnel on the right. You should be in a corridor with another corridor to your right. Go there. In this corridor there should be a grunt. He won't shoot you or anything. Go up to him and see what he has to say.