Jaquandor did the heavy lifting and kicked off this list’m and mark’m meme pulled from John Scalzi’s new book The Rough Guide to Sci-Fi Movies wherein Scalzi provides

The Canon: Reviews and commentary on the 50 science fiction films you have to see before you die (more on this in a minute)

You know the routine: the one’s in bold are ones I’ve seen (it’s possible that I’ve seen a few of the unmarked ones and just don’t remember’m):
Akira
Alien
Aliens
Alphaville
Back to the Future
Blade Runner
Brazil
Bride of Frankenstein
Brother From Another Planet
A Clockwork Orange
Close Encounters of the Third Kind
Contact
The Damned
Destination Moon
The Day The Earth Stood Still
Delicatessen
Escape From New York
ET: The Extraterrestrial
Flash Gordon: Space Soldiers (serial)
The Fly (1985 version)
Forbidden Planet
Ghost in the Shell
Gojira/Godzilla
The Incredibles
Invasion of the Body Snatchers (1956 version)
Jurassic Park
Mad Max 2/The Road Warrior
The Matrix (I like it a little bit less each time I watch it.)
Metropolis
On the Beach
Planet of the Apes (1968 version)
Robocop
Sleeper
Solaris (1972 version)
Star Trek II: The Wrath of Khan
Star Wars Episode IV: A New Hope
Star Wars Episode V: The Empire Strikes Back
The Stepford Wives
Superman
Terminator 2: Judgement Day
The Thing From Another World
Things to Come
Tron
12 Monkeys
28 Days Later
20,000 Leagues Under the Sea
2001: A Space Odyssey
La Voyage Dans la Lune
War of the Worlds (1953 version)
Oh yea, where the hell is Serenity? Well, I guess we have to read the book:

No, Serenity didn’t make the list. Deal with it (it is in the book, though. Page 24. Big shout-out to Joss Whedon there, too, although I don’t have very nice things to say about his Alien Resurrection script when I review that movie on page 59. Please don’t hurt me, Whedon fans).

I won’t argue specifics without reading what Scalzi says. Suffice it to say, for now, that as a movie Serenity runs circles around quite a few of the flicks on this list. On the other hand we may not have Serenity if not for all those that came before.