The Rules:

1. Must have been a commercially released film.
2. The work must propose an alteration of reality or a projection into the future; sci-fi/fantasy/woo-woo are all acceptable.
3. It must intentionally be comedy, spoof or satire.
4. Series counts as a single nomination.

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Keeper of the Jabberwock

Princess Bride and Galaxy Quest spring to mind.

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Gillian

"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"

"You can't erase icing."

"I can't believe it doesn't work! I found it on the internet, man!"

Dr. Strangelove. It is borderline sci-fi with the doomsday device. Definitely on the speculative side.

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Keeper of the Jabberwock

Spaceballs, the Movie.

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[Dr. Horrible]___________________________[Penny]
Listen close to everybody's heart________And you believe there's good in everybody's heart
And hear that breaking sound_____________Keep it safe and sound
Hopes and dreams are shattering apart____With hope you can do your part
And crashing to the ground_______________To turn a life around

I liked all of those.

Okay, I can think of a lot of these. Here's some of the better ones (in my opinion, of course):


The President's Analyst

Sleeper

Real Genius

Young Frankenstein

Monty Python's Holy Grail

Adventures of Baron Munchausen

Weird Science

Shrek

The Incredibles

Defending Your Life

Ghostbusters

Edited to add:

Back to the Future

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I say there is an invisible elf in my backyard. How do you prove that I am wrong?

Disclaimer: Avatar is not an official NASA image and does not imply any specific interplanetary or interstellar capability.

The Leif Ericson Cruiser

Lots of good ones already.

I'll add Groundhog Day

A personal favorite of mine.

Woody Allens "Sleeper"

The Big Bus

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There we were in the park when suddenly some old lady says I stole her purse..... I chucked the professor at her but she kept coming..... So I had to hit her with this purse I found.
-- Bender

Dark Star might be a dark horse candidate.

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Chance favors the prepared mind.
De gustibus non est disputandum.
Never attribute to malice that which can be adequately explained by stupidity.

"The Fifth Element"

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"An armed man is a citizen
An unarmed man is a subject"

Robert A. Heinlein

2001: A Space Travesty

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Never let the facts get in the way of a good story, people want to be entertained.

Pirates of the Caribbean
The Incredibles
Robots

Unfortunately removing Free Enterprise. Unless the version of Shatner in that movie counts as alternate reality.

Gillianren read my mind...

For its clever (and I think unsurpassed) spoofs of sci-fi cliches, I say "Galaxy Quest" ftw!

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"Call me old-fashioned, but I think fire is magic. And it scares me a lot."

--The State

So many good ones suggested. How about I just second Young Frankenstein.

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Sue ikki
mi hatenu yume no
hotsure kana---Choko
(This final scene, I
I will not see to the end.
My dream is fraying.)

Thanks for posting all of my picks

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"I have this theory that the Apollo missions were faked when NASA found out that general relativity was wrong because the Earth was expanding due to the Sun's iron core being influenced by magnetic waves from the electric universe after being perturbed by Planet X and thereby causing global warming. Where should I start a thread about this?" ~ ToSeek

"Those are the people that wonder how a thermos knows whether to keep something hot or keep something cold." ~ NeoWatcher

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If our brains were simple enough for us to understand, we'd be so simple we couldn't

QQR

Not as good as Airplane!, though. But A2 is sci-fi, A! isn't.

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Keeper of the Jabberwock

Lots of good suggestions.
I'll add Evil Dead 2 & 3

Bill and Ted's most excellent adventure, of course. Party on dudes!

Oh, and Gremlins.

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N6MAA10816
Faber '62 ΔTX
Are you a Bright?

Ice Pirates
Men in Black
Spaced Invaders
Mars Attacks
Time Bandits

only because Princess Bride and Spaceballs were already mentioned.