Let's make it clear up front: We'll not discuss Alien, Independence Day or Starship Troopers. When any aspect of a mega-production like these comes up short, its producers simply ladle salvation from a bottomless pit of cash that the makers of the films on our list could scarcely comprehend. Budget notwithstanding, each and every film listed below had an IDEA at its crux. The end result may have been less than hoped for, but fantasy films should be about ideas. Pounds of putty with a silicone shine should be secondary:

Honorable mention: The Astounding She Monster (1958)
I cannot defend the fact that I enjoy this film, and I won't even try. It's all about a stripper from space in a sequined suit who crashes Robert Clarke's mountain cabin. Clarke has recalled that, in her first scene, the busty alien's spangled leotard split open, forcing Shirley Kilpatrick to back out of every scene in which she appeared.

10. Invaders From Mars (1953)
The definitive B film cast (Arthur Franz, Morris Ankrum, Leif Erickson, Robert Shayne, Hilary Brooke) nevertheless play second fiddle to director William Cameron Menzies' surreally streamlined visuals. Kid-star Jimmy Hunt is our surrogate in this childish vision of a red planet invasion.

9. War of the Worlds (1953)
Producer George Pal's best film still packs a frightening punch today. Its color-splashed depiction of a relentless alien invasion is top-notch fantasy filmmaking. Genuine suspense is enhanced throughout by a credible cast and pioneering special effects. So what if you can see the strings?

8. Invasion of the Body Snatchers (1956)
Much has been written on the socio-political ramifications of Don Siegel's tension-wracked film. Forget that. It's a crackling good paranoiac potboiler about seed pods making obedient vegetables of the whole human race. Still scary after 40 years.

7. Earth vs. the Flying Saucers (1956)
When it comes to guilty pleasures, watching the nation's capital being obliterated by soaring saucers mounted with death rays is curiously untoppable entertainment. The aliens themselves are tin-covered, wizened weaklings. The climactic saucer battle staged by effects wizard Ray Harryhausen is unforgettable.

6. It Came From Outer Space (1954)
Sci Fi's pioneering producer William Alland cooked up the classic notion at the core of this film. Fleshed out by Ray Bradbury, Alland's tale of aliens crash-landing in the Arizona desert is one of his finest. This film's intelligence and crisp execution place it squarely on the list of the era's most memorable films. Set amid the spartan isolation of the southwestern desert, it's quite well-acted and occasionally very scary.

5. IT! The Terror From Beyond Space (1958)
This film is only recently being acknowledged as a bare-bones run-through for Ridley Scott's Alien. Director Ed Cahn churned out B films relentlessly, but this one is invested with a degree of energy not found in the bulk of his work. Ray "Crash" Corrigan in a Paul Blaisdell rubber suit sneaks aboard a spacecraft bound earthward from Mars. This vampiric Martian sets about stalking the crew through dark corridors and air shafts (sound familiar?).

4. 2001: A Space Odyssey
When it comes to chronicling alien encounters, Kubrick's influential masterwork may never be outdone. This one-of-a-kind film turned traditional Hollywood storytelling on its ear with its daring, leisurely pace and hypnotic visuals. Disguised as a sci fi adventure story, the film audaciously goes about reassessing the philosophical origins of civilization. Whew.

3. The Day the Earth Stood Still(1951)
Certainly in the running as the most influential film on the list, this timeless tale of a Christ-like emissary, his intentions regarded with ignorance and suspicion, ranks as among the very best sci fi tales ever filmed. The script easily balances its engaging political message with the good old-fashioned scary stuff that puts 'em in the seats.

2. The Man From Planet X (1951)
Director Edgar Ulmer and crew wring a million dollars worth of atmosphere from the most modest ingredients imaginable. Palpable, dripping atmosphere is the key to this film's success. Rarely has more been done with less. A stalwart cast led by Robert Clarke meets the big screen's first otherworldly visitor, sustaining a note of genuine credibility amid what were surely trying production conditions. The alien ship, of Ulmer's own design, is incomparable.

1. The Thing From Another World (1951)
Nearly 50 years after its release, this one's never been topped. This textbook thriller hasn't a single dull moment, it's ensemble castwork and crackling pace are without peer. Fleeting scenes of the snowbound Thing, thrashing about with sled dogs chomping at his flaying arms live in memory long after the film's conclusion. The epiphanic moment when the research term determines the circular shape of the ice-embedded alien craft makes for one of the unforgettable moments in sci fi.

And for the heck of it, here are perhaps the five worst:

5. Red Planet Mars (1953)
Check out the cast list: Peter Graves, Andrea King and God -- No kiddin'. Scientist Graves, sequestered with wife and child in his lab, has been receiving friendly overtures from Mars. When news of the Martians' prosperity and peaceful way of life spreads earthward, the worldwide economic scene is shattered. Exactly why, I don't claim to know. Are the Martian emissions the work of communists (get it? RED planet?) or are they the very word of God as the voice claims?

4. Phantom From Space (1953)
As legendary director Billy Wilder's mantel sagged with Oscars, his brother, W. Lee, turned out humorless shock films like Man Without a Body and Bluebeard's Ten Honeymoons. Phantom From Space might just be his most unabashedly deadpan effort, chronicling the brief life and awkward death of a speechless, invisible visitor who holes up in the Griffith Observatory.

3. The Cosmic Man (1958)
Take The Day the Earth Stood Still, remove the budget, the script, the atmosphere and the stars and what do you get? ... The Cosmic Man. Wearing its heart on its frayed sleeve, this paper-thin, no-budget message thriller features John Carradine and his booming baritone as an ambassador from another world whose mission of peace is misunderstood.

2. 12 To the Moon (1960)
A quirky international cast, Tom Conway as a Russian scientist prominent among them, is Luna-bound on a mission of research and peace. Upon landing, bizarre mishaps plague the party. It seems the Lunarites, whom we never catch a glimpse of, are less than genial hosts and order the party's ouster. Oddly, the moonfolk communicate through Chinese writing that only the Asian member of the crew can decipher. In a snit, the moonies have covered the earth with ice. The only solution this team of crack scientists can arrive at is to thaw the planet with atomic explosions.

1. Missile to the Moon (1958)
Director Richard Cunha gave us Giant From the Unknown, Frankenstein's Daughter, She-Demons and others, none of them very good, all of them perversely interesting. Why he chose (or was told) to remake Cat-Women of the Moon is anybody's guess. To make a worse film of it is more remarkable still. Grafting a juvenile delinquent element to its already preposterous plot was, to say the least, risky. Former Warner's contract player Richard Travis leads a quarrelsome band including Tommy Cooke (Teenage Crime Wave) and Gary Clarke (How to Make a Monster), encountering rock men, dancing chicks and the same moth-eaten spider puppet that saw service in the original film.