Entering into the best of the best category in regards to cheats and easter eggs has to be Halo 2 for the Xbox console. If you have an Xbox, there is no doubt that you have seen, heard of, or possibly even used some of the glitches. Granted, there are glitches within the game that will totally ruin the online game play over the Xbox Live network, but offline, these easter eggs and glitches are a treat, and offer some of the funniest moments in my gaming experience to date; not to mention the tricks for getting more ammo and supplying your squad with better weapons.
I think perhaps the best easter egg in the game has to be Grunt's Birthday Party Mode. When you pick up the skull it will say Grunt Birthday Party on the screen. Now when you kill a enemy with a projectile weapon, they will blow up like a plasma grenade was stuck to them. Definitely some good stuff in the game!
I am actually one of those oddball Xbox owners who don't think Halo 2 is the best game on the system, but when it comes to cheats and glitches, it filled, so it gets top pick status on Xbox cheats at Video Game Strategies. Take a peak at the Halo 2 Cheat Codes and see for yourself.