Brazil (I can only count this by virtue of equating "seen" with "having been in the same room when it was on". It was so long ago that I remember nothing from the movie. In fact, I may even be thinking of the wrong movie entirely. So on second thought, scratch that.)
The Matrix (Loved it when it came out. I liked it a little less every time I watched it afterwards. I got the second one from the library a while back, and I actually fell asleep in the first half hour, and it wasn't one of those nights when I had gone to work at 5:00 a.m., either. I've never looked back, either. For additional hatin' on The Matrix, check out 50 reasons to reject The Matrix, which includes the following:
You've worked as a policeman your whole life, protecting the innocent, enforcing the law. You retire with honors, then take a job as a security guard, working the metal detector on the ground floor of a skyscraper in order to help pay for your wife's arthritis medication. You're sitting there, on a slow day, reading your newspaper, when a girl walks in wearing a trenchcoat. She issues no demands, no warnings, no "freeze" or "drop your gun." She just tears you in half with a spray of machine-gun fire, then does cartwheels along the walls while killing all your friends.
The Fifth Element (Good movie, but man, is it weird. And I've never understood people who insist that this movie is a great work of genius, with that unimaginably irritating character in it, and yet also tell me that Jar Jar Binks is too evil to let stand.)
Star Trek: The Wrath of Khan (I suppose, but I still think it's overrated. But hey, KHAAAANNN!)
Star Trek IV: The Voyage Home (Good movie and all, but is it really indispensible geek viewing? Really?)
Serenity (Out of purism, I won't watch this until I've seen all of Firefly. I know they say you don't have to have seen the show to grok the movie, but I'm gonna do it right.)
12 Monkeys (I liked it a lot. But I have to be in a special mood for Terry Gilliam. Same as I have to be in a special mood for Wild Turkey jello shots.)
Shaun of the Dead (You know, I like reading horror, but I'm not a great fan of movie horror.)
Darkman (Wow! One of the funnest nights ever in college involved this movie. We did one of our "Three movies and a bunch of beers" nights, and this one was the second movie. Most times the second movie ended up being the most fun, since that movie always occupied the "sweet spot" when we'd consumed enough beer to understand the plot and still laugh uproariously at horribly inappropriate stuff, like when the bad guy chastises an underling by cutting off his fingers with a cigar clipper, or when the hero coerces a baddie to give him information under threat of death -- and then proceeds to kill the guy anyway. "Wait! I told you what I knew!" "I know you did -- but let's pretend you didn't!" Oh, and Liam Neeson rocks.)
Army of Darkness
War Games (Incidentally, this was the last time I liked Matthew Broderick in anything. And even then I didn't like him that much. A nerd like that, going out with Ally Sheedy? GAHHH!)
Monty Python and the Holy Grail (Well, duh! And check out the complete script, which includes a lot of different stuff from what actually ended up in the finished movie. For instance, here's a bit that would have taken place just after the Bridge of Death, when Arthur and Bedevere are coming to the boat that will take them to the Castle Aggghhhhh:
Suddenly the air is filled with ethereal music, and out of the mist appears a wonderful barge silently and slowly drifting towards them. They gaze in wonder. The mysterious boat comes to where they are standing. As if bewitched, they find themselves drawing closer to the boat. As they are about to step in, a ragged figure looks up at them.
BOATKEEPER: (he is the same as the BRIDGEKEEPER and the SOOTHSAYER) He who would cross the Sea if Fate, must answer me these questions twenty-eight.
He fixes them with a baleful eye, ARTHUR and BEDEVERE exchange glances, then turn, with minds made up, pick him up bodily and throw him in the water. They climb into the boat and the boat moves off into the mist
Office Space (They said I could keep my radio at a reasonable volume.)
Repo Man (I don't know the first thing about this movie!)
Jason points out a number of movies that could also be considered "Essential Geek viewing"; I'd add The Abyss and Superman to the list. Another? Well, it's not a SF or horror flick, but neither is Office Space, and I've never met a single person that I held to be a Geek in Good Standing who hadn't seen The Karate Kid.