Aliens, Vulcans, droids, Replicants and something called a "Dennis Nedry" are all represented on this list of our 25 favorite sci-fi movies. We searched through our catalog of science fiction's best, the ones that make up our nerd and filmgeek bedrock, and assembled a list that showcases the genre.

Sorry, X-Men fans, but no comic book movie titles allowed; just those films that are easily found in the sci-fi section of the video store. (Besides, you can check out our picks for the best Comic Book Movies if you want to know where Marvel and DC ranks.)

Our criteria? Well, aside from being just a great piece of moviemaking, the Top 25 candidates required a significant impact on the genre, stories and ideas that raised the bar on what good moviemaking can be, pop culture reaction, originality and Editor's Choice.

Less reading, more debating about our number one pick!

When your dad built his career singing about wayward astronauts named Major Tom and spiders from Mars, science fiction just runs in the blood. Duncan Jones carried on the family legacy with Moon, a unique science fiction film that proved to be one of the surprise gems of 2009.

The setup of the movie is elegantly simple. The vast majority of the film features only one actor, Sam Rockwell. Rockwell's Sam Bell is a lone technician on a mining station on the moon. With communications with Earth spotty at best, his only source of companionship is the helpful robot GERTY, voiced by Kevin Spacey.

The film makes startlingly effective use of its limited cast and equally limited set locations. Viewers grow to care for Sam as he struggles with his claustrophobic surroundings, mounting paranoia and hallucinations, and finally the surprise twist that throws him for a loop. Clint Mansell's musical score helps generate an impressive atmosphere as well. If science fiction is about exploring what it means to be human, then Moon is one of the better examples to come along in recent years.

When director Neill Blomkamp and producer Peter Jackson's planned Halo movie fell apart, the gaming world's loss was the sci-fi arena's gain. The pair's apprentice/mentor relationship instead brought them to create District 9, one of the best aliens-live-among-us pictures ever made.

As with all great science fiction, the story of District 9 is an allegory for some of the real-life issues that humankind is facing in the here and now. It's a very thinly veiled allegory, yes, but still a quite effective one. Sharlto Copley is perfect as Wikus van de Merwe, the cluelessly racist bureaucrat who is charged with clearing out the titular alien internment camp -- the zone where millions of displaced insectoid extraterrestrials have lived for decades.

Full of crackerjack action scenes and visual effects, this film seemingly appeared from out of nowhere to stun genre fans and remind us that great sci-fi can still happen, giant robot movies notwithstanding. In fact, District 9 finally proves that great sci-fi movies can have giant robots in them. Thank God that Halo movie never happened.

An alien with the ability to take the form of any life that it absorbs infiltrates an Antarctic research base, and soon the 12-man team is up to their eyeballs in slaughter, suspicion and paranoia. John Carpenter's best film has itself planted on either side of the horror and sci-fi movie lines.

As a horror film, The Thing would rank higher than it does on this sci-fi list that boasts some heavy hitters in the genre. As a sci-fi film, a cross between Alien and Invasion of the Body Snatchers, the movie succeeds at asking the question "Who Goes There?", much like it's literary source material did, by forcing our survivors to figure out who they really are as The Thing puts their humanity to the test. The tension escalates and Kurt Russell gives one of his best performances as team leader MacReady.

The practical special effects hold up better than you'd think (save for the stop-motion Blairmonster), and we defy you to not have your mind blown when the head of a victim sheers itself from its burning corpse and spider-walks away. If you haven't seen this movie, then remedy that now.

Avatar is a movie a few people love to hate, while everyone else spends every free moment at the theater re-watching it. Officially the highest-grossing movie of all time, Avatar succeeded on multiple fronts. It was the first true showcase for what 3D could bring to the theatrical experience, using it as a storytelling aid rather than a cheap gimmick or a crutch. Undoubtedly, Avatar is one of the most visually thrilling and beautiful films ever made.

But Avatar also succeeds because of its simple, engaging story. Yes, the script is a bit too simplistic at times in its portrayal of the noble, nature-loving Na'vi and the evil, greedy humans. Yes, we essentially watched the same story unfold in Dances With Wolves 20 years ago. But we have never seen that story told in space, with the awe only a Cameron film could deliver. Avatar is a story about a man who went in search of a new life and found the happiness he long craved. That's something humans and blue cat people alike can appreciate.

"Hold on to your butts." Thanks for the warning, Samuel L. Jackson.

You know why this movie still works, more than 15 years after it unleashed the power of CG everything on audiences? Because when Alan Grant first looks up to see that veggiesaurus get on its hind legs to eat some tree leaves, the scene still gets us to mouth "wow" every time.

That sense of awe and wonder that only a Spielberg movie could provide is the reason why we still get geek goose bumps when Hammond says, "Welcome to Jurassic Park."

When this movie first premiered in the summer of 1993, it spared no expense at treating audiences to a then-groundbreaking blockbuster experience. Sure, CG technology has advanced since ILM's pioneering work here, but the movie's achievements within the medium – for better or worse – are what helped pave the way for those innovations. While the story about Dino experts and one twitchy, snarky Jeff Goldblum forced to survive a Disneyland ride gone all murder-y is a clothesline by which Spielberg can hang set pieces on, it does deliver just enough emotion and character work to elevate the film above simple popcorn entertainment.

In fact, it makes it one of the genre's best examples of popcorn fare, a sci-fi tale that reminds man for the millionth time that he should never play God, especially if he thinks anything good can come out of employing a man named Dennis Nedry.

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