It could be just a look or even the slightest body movement that greatly contributed to a role, etc. I think the winner is Al Pacino in The Godfather when Kaye tells Michael that she aborted his child. The look of intense fury in Pacino's eyes still unnerves me every time I see it.
"I hear there's rumors on the internets" - George W. Bush
5. "Mos Def in Brown Sugar" In response to Reply # 0
There's a moment when Taye Diggs comes out of the radio offices looking dejected. Mos looks at Taye and then has this amazing look of disappointment. That moment sold me on Mos' acting ability. Absolutely great moment in a film that's, well, not so absolutely great.
"Your current frequencies of understanding outweigh that which has been given for you to understand." Saul Williams
7. "RE: What's the best non-spoken acting in a film?" In response to Reply # 0
Pacino's minimalism and what he achieves with his eyes in "Two" is astounding. What's coming to mind now are his scenes with Senator Geary in his home office and with Tom when Michael gives Tom an ultimatum when they were discussing whacking Roth at the airport (I think that's what it was).
12. "at the end of the wrestler (spoilers)" In response to Reply # 0
at the end of the wrestler before mickey jumps off the top ropes
man, that look in his eyes is the most bittersweet stare i have ever witnessed, whether in film or real life that look spoke a thousand words and emotions at the same time internally, i sort of felt like crying when i first saw it
14. "Heath in The Dark Knight, muted police car scene" In response to Reply # 0
Heath Ledger in The Dark Knight, police car scene, when the sound is muted and all you see is Heath's head sticking out of the police car window, taking the air in and looking outside, very much dog-like
29. "Michael nutting up before blasting Solazzo & The Cop" In response to Reply # 0
In Godfather I. Watching his eyes dart around and around as he's steeling himself up for what he's about to do. You can almost hear his thoughts, "Am I really gonna do this???"