Great lists here, found some cool new recommendations to check out. I like the broad definition of sci-fi being used by everyone and I think I can defend all of these as being sci-fi enough:

1. Metropolis (1927)
2. 2001: A Space Odyssey
3. Robocop (1987)
4. Little Shop of Horrors (1986) - particularly with the original invasion ending
5. 20,000 Leagues Under the Sea
6. Solaris (1972)
7. Akira
8. Alphaville
9. Re-Animator
10. Tetsuo: The Iron Man

Honorable mentions to Stalker, The Terminator, The Andromeda Strain, La Jetée, 12 Monkeys, Brazil, Forbidden Planet, Blade Runner, Videodrome, Paprika, The Thing, Battle Royale, Dark City, Star Trek: TMP, and lots of kaiju movies.

Forgot about nuclear war movies. Love Threads and A Boy and His Dog. The Atomic Cafe is great too.

I need to see I Am Legend again but I wasn't into it much when I saw it at release. I do love the Omega Man and Last Man on Earth versions of the story.

28 Days Later was great, another one I haven't seen since release though. Been meaning to watch The Road and World War Z so thanks for the reminder.