The Day the Earth Stood Still
Howard Hawks' The Thing From Another World
Producer George Pal's Destination Moon, When Worlds Collide, The Time Machine, The War of the Worlds, and Conquest of Space.
Ray Harryhausen's effects work in The Beast From 20,000 Fathoms (1953), Earth vs. the Flying Saucers (1956), and 20 Million Miles to Earth (1957), Mysterious Island (1961), First Men in the Moon (1964), One Million Years B.C. (1967) and The Valley of Gwangi (1969)
Them! (look for Aliens similarities)
Invasion of the Body Snatchers
On the Beach
The Quatermass series and films
This Island Earth
Forbidden Planet (an inspiration for Star Trek)
The Angry Red Planet
First Man Into Space
It! The Terror from Beyond Space (Precursor to Alien)
Gojira
20,000 Leagues Under the Sea
Journey to the Center of the Earth.
2001: A Space Odyssey
Planet of the Apes
The Last Man on Earth
Planet of the Vampires
Fantastic Voyage