I'm going to date myself here, but Nickelodeon was fairly new when I was watching, during the "silver ball" period. You Can't Do That On Television was one of my favorites, but the young nerdling in me totally gravitated to The Tomorrow People. Mysterious Cities of Gold and Belle and Sebastian were good when they added them later. They had all sorts of other odd little programs like The Third Eye and Into the Labyrinth that were okay, but I don't remember caring for them quite so much. Mr. Wizard's World was endlessly cool, of course, and I still want my own supply of lycopodium powder.
I don't remember if they actually had real commercials to begin with, but during breaks they had things like "The Vocabulator," which was kind of an oscilloscope display with a voiceover that taught a word-of-the-day sort of thing, and puzzle kinds of shorts about finding pirate treasure and such, though the selection was so limited you would see the same ones all the time.
I was sort of outgrowing Nickelodeon anyway by the time Double Dare turned into a huge hit and they rebranded themselves with the orange splat, but they still try to drag me back now and again with things like Ren & Stimpy and Invader ZIM. I think they're probably going the route of getting more and more bland over time, so such subversive fare is less likely to slip past S&P and onto the air.