The moment willy wonka met the children in the original. Family feud with steve harvey Surprize guest performaces at concerts
Almost all of Seinfeld. I've been watching them again with the notes about nothing. From what I can gather they had a basic script to follow but a ton of it was just made up on the spot etc or it never happened how it was written. I usually don't watch those sorts of special features so I'm not well informed of such things in movies.
I think one of the best is Heath Ledger. The cell scene he starts clapping, and when he shakes the detonator. I love actors that get so absorbed in their roles, those make for the great ones.