What is Your Favorite Video Game Cheat or Exploit?

My personal favorite cheat is the Medal of Honor: Frontline's Men with Hats cheat. Killing Nazis with Submarines for hats made me tolerate the average gameplay?

Do you have any fond memories of cheats or glitches that improved the game you played?

NES / SNES / Genesis - Pick a game - Level select

Didn't get any better, Ahhhh Nostalgia

idkfa

Alternatively, one of the many Siglemic does in each Super Mario 64 speedrun he does.

There are so few cheats for games nowadays that I can think of. I liked how in Super Mario Kart, you could shoot a red shell a little bit away from your opponent, and if he was sitting still, it would just keep circling him.

I have some fairly fond memories of the many Halo 2 glitches (sword jump, super bounce, etc).

The guns and armor cheats in GTA were always a lot of fun.

I always enjoyed exploiting maps in Call of Duty and CoD United Offensive back in the day. Ledge jumping and finding away out of a map, whether it was the developer created maps or user created maps, was always fun. Got to the point that I was testing maps for people to see if there wasn't anything that could be exploited. Fun stuff.

I quite liked the egg glitch in Resident Evil 5. And the combination of items that makes you invincible against Dracula in Symphony of the night... It's like a staff and a sheild combo or something.

I had shit loads of fun with the all weapons, armor, and health cheats in the GTA games.

There was this one for I believe the NES. I can't recall the game or even the cheat, but I remember it required down to be held on the second controller, which I accomplished with a piece of tape. That's my favorite for the bizarre setup alone. 
 
Oh, and also Game Genie. 

@Little_Socrates: That Zelda speed run was amazing! I had no idea there were so many exploits in Ocarina of Time.

@insouciant: Yeah, it's absolutely crazy stuff. Some of the things Sig does on a 70/120 star run in SM64 come close (though it might pretty much begin and end with the first star exploit with the bob-omb.)

Man alive if that post-Gohma stuff is anything but too much to handle.

I have fond memories of the Halo 2 glitches and all of the Grand Theft Auto cheats.

My buddy had one of those Game Genie dealies for the N64, let you play multiplayer in the locked off bit of the Facility level (i.e. the bit with the exploding gas canisters at the end of the level in single player). I don't really know why but that absolutely blew our minds as kids.