There weren't any really notable moments until fairly recently when I used the bad clone glitch to transform a Sneasel into a Celebi knowing Fire Punch, among other potentially useful moves. It was all done without a cheating device, and I definitely thought it was pretty neat.
I suppose for credibility, I should add that it can be found here.
Most probably first fighting a Yanma (I was 8 years old, I thought the name was weird and my game had turned Japanese) outside Goldenrod city. Also, it would be finally catching those legendary dogs without master balls... last week.