The Boys from Brazil and The Odessa Files. Enough historic reality set to current times for when they were released to be scarry as hell and ask yourself could it really be.
But if we shift to Terror, by far, watching Wait Until Dark in a darkened room on a big screen where that's the only light, should scare the bejeezus out of you at the climax.
Soylent Green, the first Planet of the Apes movie, and the Omega Man and The Andromeda Strain.