I'm no expert besides the fact that I watched the film once a year as a child. Dorothy turns to her dog Toto after the tornado knocks them into Oz and says "Toto, I don't think we're in Kansas anymore." All the kids loved that line. Lots of iconic lines simply because it was a shared generational experience, I think.

I also should mention a bizarre coincidence (?) Some people believe Pink Floyd's Dark Side of the Moon was oddly synced to the scenes of the film. It's pretty entertaining. Just go on YouTube and search Pink Floyd Wizard of Oz. Yes, we were pretty altered in the 70s.