The term "classic film" usually refers to enduring works of timeless quality. But not always. Sometimes, a film comes along that's so inept, so unintentionally hilarious, so unspeakably terrible, that it achieves timelessness - movies so bad they're good. These science fiction films will never enter the National Film Registry, and they won't show up in the history of the Oscars. But if you want an easy laugh while eating popcorn with your friends, these might be some of your best bets.
1. Attack of the 50-Foot Woman
Woolner Brothers Pictures
Nancy Archer's husband gives her no respect. He's mooching from her millions, and openly dating a floozy in the local dance hall. But after Nancy encounters a strange object on the way home, she goes through some big changes. And she'll never be disrespected again. 
Rumor has it that Attack of the 50-Foot Womanwas tens of thousands of dollars under budget. It shows. Check out the special effects. The alien is so poorly projected he's actually translucent, and Nancy's giantess hand is obviously papier-mâché. But all is forgiven when the enraged heroine bursts through the roof of her house to hunt down her husband. Nancy's destruction of the not-to-scale dollhouse built to contain her is one of the iconic images of B-movie history.
2. Barbarella
Dino DeLaurentis Cinematografica
From the first shot, in which Barabarella (Jane Fonda) floats nude and nubile in outer space, the elements of the film are clear: sexuality and terribly dated late-sixties excess. What other decade could have produced a space shuttle upholstered entirely in shag carpeting? Based on a comic book, the film is episodic and nonsensical. Marcel Marceau, the great mime, is the brilliant-but-weird Professor Frink, and John Phillip Law plays Pygar, the blind angel who's lost his will to fly. (Guess how Barbarella inspires him...) By today's standards the film is pretty tame, but you should probably put the kids to bed before this one or you might have to answer some very complicated questions. Free love has never looked so ridiculous.
3. Plan 9 From Outer Space
Reynolds Pictures
It's almost unfair to include director Ed Wood's Plan 9 From Outer Space. Incompetent, wooden, and nonsensical, Plan Nine achieves a transcendent badness few schlock films can approach. Bizarre narrator "The Amazing Criswell" can't tell us whether the film occurs in the future or the past. Scenes change randomly from day to night and back again. Props are made from barely disguised cardboard. Bella Lugosi (sadly at the end of crumbling career) actually died during filming and was replaced by Wood's wife's chiropractor, who bore not the slightest resemblance. After you've laughed your way through Plan Nine, check out Tim Burton's Ed Wood, a loving, touching biopic of the worst director in film history.
4. Queen of Outer Space
Allied Artists Pictures
Three astronauts crash on Venus (the female planet, natch), to find the women have seized total power, ending the destructive warfare of their male predecessors. So, of course these peaceful women have created a death ray to eliminate the meddling, boorish men of Earth. (A film historian once said: "It almost sounds feminist, until you see it." In classic '50s style, the women wear ball gowns and high heels at all times. Zsa Zsa Gabor plays an unconvincing scientist, dripping with diamonds. And for a sisterhood of strong-willed women, they sure go gaga for the first square-jawed astronaut to come along. Watch for the hilarious, densely Freudian line "Even if women could invent such a ray gun, how could they aim it?"
