There are certain movies that I consider classics in the SciFi genre:
Star Wars: A New Hope
2001: A Space Odyssy
Silent Running
Soylent Green
Planet of the Apes
Invasion of the Body Snatchers
The Abyss
Day of the Triffids
The Thing (John Carpenter's)
The Day the Earth Stood Still
War of the Worlds (Byron Haskin's)
The Matrix
The Invisible Man
King Kong
Frankenstien
The Time Machine
Jason and the Argonauts
Night of the Living Dead (might actually be Horror genre)
Close Encounters
Alien
Blade Runner
Predator
What would you add?