Leaving to the side the various obvious Arnie and Stallone and Lundgren picks:

The infamous skull-crushing scene in the original Blade Runner. In fact the movie is replete with scenes that demonstrate the unearthly physical power of the NEXUS-6 Replicants, but that one is the most terrifying and memorable and Rutger Hauer and Joe Turkel work together to sell the emotional freight of that horrific moment to perfection.

Highlander, the original film. Clancy Brown's Kurgan is frightfully strong, as he particularly demonstrates when he runs a man through the gut with his sword, lifts him up by it like he was a feather, and casually tosses him aside.

Fezzik in The Princess Bride for a more comedic and light-hearted version. He tosses boulders around like baseballs, can knock an oak door down with a single blow of his fist, can haul a group of people up a cliff face with raw power, and even knocks a guy out cold when he's just trying to gently tap him.

Khan in Star Trek 2: The Wrath of Khan. Yes, Montalban's incredible physique in that movie is authentic, and helps to sell moments when he lifts fallen bulkheads off of downed comrades or effortlessly holds Chekov aloft with a single hand in a moment on Ceti Alpha V right before he does something much more horrible to him.

Unbreakable. I see that the weightlifting scene has already come up, but for me the more awe-inspiring moment is when he attacks and chokes out an absolute massive beast of a man (who is hammering him with elbows and slamming him into walls all the while) through sheer persistence. Honestly, for all its simplicity, this is actually one of my favorite movie action scenes, and sells the movie's premise all on its own.

Achilles in Troy. The power of Achilles clearly derives as much from extensive skill, practice and talent as much as raw power: but he has raw power aplenty. The spear-throwing scene when he's taken the beach and Hector is riding in on him is especially convincing and impressive (although it's obviously FX), and Brad Pitt equally convincingly sells the godlike power of Achilles every time he's in combat, as he both out-skills and overpowers his opponents.

Daniel Craig in Casino Royale. The chase scene where he pursues Sebastien Foucan's parkour-master antagonist through a construction site, specifically. There haven't been many Bonds (perhaps any other Bonds) who could sell the raw power that Craig's Bond brings to that sequence, which pits finesse against sheer brute persistence. One of the very finest action sequences of all time.