Too many to mention, there’s the famed scene where Joe Pesci completely improvised the whole “Funny, how? Like a clown?” Ray Liotta looks fucking lost.
One of my faves though is nothing really special or remarkable, but it really floats my boat. If you watch Steve McQueen in The Magnificent Seven, in scenes where he’s on camera but has no dialogue, he’s constantly fidgeting, with his hat, his face, patting his horse. He said later in his career that he, being a relatively unknown newcomer, wanted the audience to notice him, their attention drawn to him even when the established star of the film Yul Brynner held centre stage.
It works, anyone who enjoys it should look out for his behaviour next time they watch the movie, like I say, nothing particularly exciting, but it works for me, impressive stuff.