Here's some ones I could think of.
Heat - Robert De Niro hears a noise from a truck full of cops staking him out. They've got him on night-vision and everyone waits to see what he does. Brilliant.
Aliens - Aliens inside the room (in the ceiling) and when the facehugger in the stasis tube slams into the glass trying to get Burke. More of a jump moment though I s'pose.
The Departed - Matt Damon phones Leonardo di CapriSun, both knowing the one on the other end is the mole in each camp, no one speaks. Amazing tension in the cinema, you could have heard a pin drop! Saw it on DVD the other day and it was just as brilliant.
Any other good ones, folks?
