The Fly: “Help me! Help me!”
The Blob: The principal (or some authority figure) hesitating with a sour look before resolutely picking up a rock to smash a window in the high school, so the heroes can get the door open and get some CO2 fire extinguishers.
Good one. The “ineffective low-calibre revolver” in the hands of the world’s bravest idiot. Then Rhedo grabs him and cliché instantly turns into real horror. That little “down the hatch” gulp nails the sequence, Ray Harryhausen at his finest.
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The lock was sold at auction. http://www.liveauctioneers.com/item/7457309
(from forbidden planet)
heh. my point. it’s why i can’t watch the Rhedo die. just too damn realistic for my softhearted tastes. 
Me too. I can watch it, but it’s definitely sad.
NGHRRUU
Or however you write down the noise Godzilla makes.
Kevin McCarthy running wild-eyed through the streets yelling “YOU’RE NEXT!” in Invasion of the Body Snatchers.
That’s Quatermass 2*, released in the US as Enemy from Space, another great 1950s treat from Nigel Kneale. The actual line is, I think, “It burns. The food – it burns”
I love the original Quatermass trilogy (not the later additions), but neither this one nor the other cited above is really well-known. I think their moments ought to be iconic, but I’m not sure they’re well known renough to be called that.
*The first film, AFAIK, since silent days to use “2” in the title, predating The Godfather II by almost 20 years.