I'm pretty sure you can jump over the flagpole in the original Super Mario Bros. in stage 3-3. I remember answering this question back in the day in Pro's Corner of Nintendo Magazine.
Another really cool trick that's almost mythical yet true is Chris Hoolihan's room in Zelda: Link to the Past. I remember that a 11 year old kid actually figured it out and sent it for publication in Nintendo magazine.
Unfortunately we credited a totally wrong person in the magazine (actually, a non-existing one). The kid still felt that "we had a connection" and kept on calling to the Hotline every day going "Hi, this is the guy that found Chris Hoolihan's room".
He became really obsessed about Donkey Kong Country after we were showing off a pre-release EP-ROM in a games event. Once he got the game, he completed it fully in no time, and then called every day to ask "If there are some new secrets found in DKC", disturbing our games of International Superstar Soccer and NHL94 (still the best).
It'd be a common prank for us to redirect this guy to an unsuspecting counsellor:
"Hey, here is a call about Secret of Mana, you know that, wanna pick it up?"
"Sure"
"Nintendo Hotline, how may I help you?"
"Hi, this is the dude that came up with the Chris Hoolihan trick..."
"FUUUUUUUUUUUUUUCKKKKK I'LL KILL YOU GUYS NOOOOOOOOOOOO!!!!"