i also used to use action replay on my ds lite
i actually owned one of these. was nice for pokemon
i used to use a trainer for club penguin that let me unlock a forgetton of items and do a bunch of other stuff.
i might have also used one for stick arena but that was eons ago
edit: also, while not hacking, toying with cheat codes on simpsons hit & run was a blast
honking to jump 20 feet in the air, zooming at 100MPH while instantly exploding any car that came into contact with me