My favorite Sci-Fi action movies seem to be decades apart.
Star Wars in 1977, Terminator in 1984 and the Matrix in 1999.
I’m sure Dopers will know if there are other sci-fi action movies worth watching.
You forgot 1992’s, Terminator 2 
Also, Aliens.
Oh, and more recently, I thought I, Robot was surprisngly good.
Bladerunner
The Abyss
Starship Troopers
Predator
Plenty of cheesier ones like Ghosts of Mars, Screamers and any number of Arnie flicks.
Any one mention Aliens?
Serenity 2005
An action movie?..Really?
I am partial to The Fifth Element.
And a lot of the others already mentioned.
I really liked Stargate.
I agree. Good art direction will forgive a few plot holes.
And many of the others. But–what about Buckaroo Banzai?
Serenity; the whole Alien series (yes, even 3 and 4); Galaxy Quest (comedy/action); Jurassic Park and Jurassic Park III (The Lost World sucks); Total Recall; all three of the Terminator movies; War of the Worlds.
Also, if you’re willing to try some anime: Ghost in the Shell; Akira; Nausicaa of the Valley of the Wind; Castle in the Sky; Final Fantasy VII: Advent Children.
12 Monkeys.
The Abyss rocks. See it. And another vote for Buckaroo Banzai. Delirious fun.
Try Dark City. It’s very creepy, atmospheric, intriguing and ultimately uplifting. And you can see Kiefer Sutherland at his most un-Jack Baueresque.
I suppose Close Encounters of the Third Kind and 2001: A Space Odyssey might not qualify as SF “action” movies, but I still like 'em a lot.
I was a little puzzled by the OP, because as far as I can tell, almost ALL science fiction movies are turned into action movies, and this is a pet peeve of mine (hey, Hollywood - just substituting a laser gun for a revolver doesn’t make it sci-fi, okay?). I think it would be easier to list the sci-fi movies that aren’t action movies.
2001
Dark Star
Solaris
The Day the Earth Stood Still
Forbidden Planet
Blade Runner
Dark City
Total Recall
Stargate
Terminator (1)
Matrix (1)
Serenity
Brazil
The Fly
28 Days Later
Gattaca
Chronicles of Riddick (I know, I’m the only one)
The Island (again, I’m alone)
Fifth Element
The 6th Day
Children of Men
Do Mad Max movies count as sci fi?
A.I.: Artificial Intelligence
Back to the Future series
Short Circuit series
The Time Machine
I thought of 12 Monkeys before rhythmonly posted, but it’s one that I personally wouldn’t classify as an “action movie,” although I guess that’s debatable.
The Last Starfighter
Robocop 1 and 2
Freejack
Men in Black
The Thing
I’ve recently discovered the works of an obscure director named Philip Cook. He makes ultra-low budget movies and he’s virtually a one-man show, tackling writing, directing, photographing, editing and special effects. But his sets have a real eye for detail and his CGI effects are dreamlike. This is clearly a man who loves sci-fi. Sure, the movies are a little rough around the edges, but I can forgive him for that. I’d recommend his movies Despiser and Outerworld. I’d love to see what this guy would be able to accomplish if someone gave him an adequate budget.
Although not very action by today’s standards,
Westworld
Saturn 5
Black Hole
Silent Running
Farenheit 451
and my namesake,
Logan’s Run
My* edit of your post - I agree with all of the above!
I’ll add:
Tron
Galaxy Quest
Minority Report
You aren’t alone! I came in here to mention Riddick, along with the fact that I figured I was the only one.