Wow.
I also recall 2 more...
When you get the rocket box in the plaza, try to get a good angle so you can see inside the bell tower (the one across the building with the Yoshi Egg) and you'll see a box inside!
And this one's hard to describe... Somewhere in the wall in the plaza where the fruit market is... There's a ridge someplace and you can slip into the wall, fall into a bottomless pit, and lose a life.
This isn't a glitch, but everyone knows that you can get to Pianta Village by spin jumping. If you can't do it, try using Yoshi's spin jump. It's a lot higher than Mario's.