You have to start with King Kong. It's the classic "giant animal" tale and has been included in the Library of Congress. The Nazi's banned it, so it has to be good.
A box-office smash (RKO's first success), it's the one everyone tried to imitate. Observe:
Wikipedia sez: "Buoyed by the enormous success of King Kong in 1933 and its profitable theatrical reissues in 1938, 1942, and 1946, RKO had great hopes for Mighty Joe Young. Upon its release in 1949, the film was honored with an Academy Award for Special Effects (a category that did not exist in 1933 for King Kong)."
Don't think it would stop there. The genre just kept growing.
If a giant gorilla is scary, then would could be more terrifying than Them! ?
Nuke it from orbit; that's the only way to be...oh. That's how they got big?
Look out, Canada!
Look out, Mexico!
Look out, England!
Look out, Jap....eh. You guys are used to it.
Ah, big silly monkey. You should not be in Japan. That's where Godzilla lives.
SEE WHAT I MEAN?
The monster is actually a giant snail. And it doesn't challenge the world as much as the Salton Sea and my lunch. Snails are just all...ugh...that's just gross. The worst part of this flick is the instruction video that shows close-ups of real snails eating. I gag just thinking about it.
Although Hans Conred puts in a nice performance here. He's like a proto-Quincy.
I'd say it was the giant bats or giant rats or the giant winged lion that made me include this, but I just wanted you to see this insane thing.
OK, giant rats. They're still scary. Good Halloween costume, if you're of a mind to.
If you go back and watch The Matrix (the first one--the good one), and check out the scene at the Oracle's apartment, this is the movie the kids are watching in the living room.
The Twin Towers? TOO SOON, MOVIE. TOO SOON.
Here's a culturally insensitive cartoon to make it all better.