I've always enjoyed seeing an awesomely well acted monologue in a movie. It's usually the time when the actor/actress is allowed to run with the dialogue and make it their own. It usually consists of longer takes then usual, and very few cuts to make the audience emotionally invested, understand, relate or feel empathy towards the character. And even though acting can be subjective, after seeing these sort of scenes, I have no idea how they could have been acted any other way.
I can think of quite a few amazing scenes, like Kevin Spacey's tear jerking retelling of how he came by his scars in "Pay it Forward" and the example I've chosen for this post. "I am Sam" is a brilliantly acted movie, and even though Sean Penn acts his pants off, and Dakota Fanning is amazing (as usual), Michelle Pfeiffer has a very memorable scene that stuck out when remembering afterwards. Here it is!