Those things that happen in games that are not supposed to happen; some are stupid, others are frustrating, some are hilarious, but what is your favorite.

Mine was somewhat of a one time glitch.  I was playing FF III for the SNES (which of course was really FF VI, but we did not know it at the time .)  The screen went all hay-wire, and then the game sort of just died on me.  I remember panicking that perhaps I was going to lose all my save data, and I was about half-way through with the game.  I turned the power off and then on, and then discovered the most amazing thing............

 My item list was just stacked with the rare and hard to get accessory items like the genji glove, and multiples of them at that!!!  My FF party was just plain stacked, and it didn't matter who I used.  I remember showing to this to my cousin, and he was just floored.

Mine was in Halo when you could drive the Ghost up the cliff and go "Outside" the level right up into the sky and snipe.... good times.

A similar glitch happened to me more than once in FFIII; getting hundreds of Paladin Shields was pretty damn cool.  I remember reading later that this kind of glitch was relatively common, and that there were actually ways to trigger it.  I never bothered to try it out myself, though.

Same here for final fantasy VI (i refuse to call it 3) I have had that glitch where it goes mad, then you get lots of items

Street Fighter 2 in the Arcade had many glitches. My favorite glitches from the game are:

1.) Invisible Throw with Guile
2.) Restart of the entire game with Guile
3.) Handcuffs with Guile
4.) Invisibility with Daslim