I found most of the glitches used in my runs by accident lol.
Examples:
Keitai Denjuu Telefang - Speed Version - Phone glitch discovered only because I was trying to get rid of the ringing (which prevents me from battle, starting conversations, etc) and coincidentally, the frame that I paused on triggered the glitch.
Densetsu no Stafy - Discovered the save glitch while messing around in real time (while still recording) and restarted the game by accident.
Wario Land II - I wasn't even trying to clip through the walls; I was trying to optimize a turn, and somehow accidentally clipped into a wall.
The SpongeBob SquarePants Movie - The speed preservation was found by chance very late into the game, causing me to redo the run several times. The OoB glitch was from an attempt to optimize a turn.
Grand Theft Auto: Chinatown Wars - I changed the camera angles for entertainment purposes, and found that it also manipulates NPC vehicles.
Spider-Man 2 I input the password coincidentally at the frame the credits trigger
Yuu Yuu Hakusho: Makai no Tobira - I was trying to improve the entertainment value of the boss fights when I discovered the special attack glitch.
Monster House - I found out the door glitch in real time, but wasn't able to replicate it until I record myself playing real time, and it just happened.