In chronological order
Metropolis
Things To Come
The Thing From Another World
The Man In the White Suit
War of the Worlds (the George Pal one)
Forbidden Planet
2001: A Space Odyssey
Colossus: The Forbin Project
The Andromeda Strain
Solaris (Tarkovsky)
Honorable mentions go to all three Quatermass films, The Monster that Challenged the World, and any film by Jack Arnold.
"Colossus: The Forbin Project" -- the only time before this that I'd heard of it, and the only time I've seen it, was for a film appreciation class in college. Interesting deviation from, say, James T. Kirk's many confrontations with engineered societies. :')
The first post not dragged down by juvenile nonsense.
Metropolis is clearly a breakthrough film and still stands up well today. The Thing (from another world) is influencial, but ironically the John Carpenter remake actually reflects the original story (Who Goes There?) better.
I'm only familiar in passing with The Man In The White Suit, but I would definitely substitute The Day The Earth Stood Still from this era. Frankly I'm surprised it's not on your list.
The Pal WOTW is one of my guilty pleasures from late night TV. It does not stand up on its own as an SF movie, except as an artifact of its era. And I dearly love it, bad acting (particularly by Gene Barry) and all. Even so I might substitute The Beast From 20,000 Fathoms from the same year.
Forbidden Planet. What can I say? Shakespeare. Anne Francis. Walter Pidgeon. Anne Francis. Leslie Nielsen. Anne Francis. Jack Kelly. Anne Francis. Richard (the 6 million dollar man) Anderson. Anne Francis. Earl Holliman. And finally Anne Francis and Robby The Robot. What's not to like?
2001: A Space Odyssey is clearly a classic, though, for me, it doesn't hold up as a movie in its own right. 2010 actually is a better movie to watch, some 25 or 30 years on.
Colossus, the Forbin Project is a perfect SF TV Movie. It wasn't, however, a TV movie. It stays very tightly within the book and does an excellent job of conveying the paranoid message of the the book. What most people don't realize is that The Forbin Project was the first book in a trilogy. Remember, if you will, that at the end of the movie Colossus the master computer was in charge and humans were enslaved. Well, in the second book, The Fall Of Colossus, those wiley humans managed to figure out a way to defeat the mighty computer brain. Unfortunately it was only as Colossus was failing that they found out that the great computer had only done what it did out of necesity, since it didn't have time to deal with petty human squabbles while it prepared to fight off the alien invaders it had deduced were about to arrive. That is the subject of Colossus And The Crab. Totally different object lesson to be drawn from the full trilogy than from the stand alone first story. I'd love to see SciFi do them as a mini-series.
Andromeda Strain is very well executed and absolutely pure speculative fiction (not SciFi). It stands out, for me, in this list. Unfortunately its not a real fun movie to watch. Oh well.
Tarkovsky's Solaris (as opposed to George Clooney's) has its attractions, but it's too obscure for me.
Now, I'm preparing my own, definitive, list (;^>) but I definitely give you credit as the best so far in this thread.
I really think I'd love sitting down in a good movie theater / bar (ala the Alamo Drafthouse in Austin) sometime. You have very good taste.
The Day the Earth Stood Still.