Aladdin: Jafar does a textbook example of the rundown of this trope, wishing to become an all-powerful genie. In his following exultations, he mentions how the universe is now his to control, even going so far as to create a small solar system between his hands just for the hell of it. This is until Aladdin reminds him what the other half of "phenomenal cosmic power" is... "itty bitty living space".
Skeletor has one of these speeches at the climax of the Masters of the Universe live-action movie, right down to the line "I am a god!"
Groundhog Day. After reliving the same day over and over again, and attempting suicide in a vast number of different ways, Phil eventually concludes that he's God, then tentatively adds, "Not the God. Just a god." (He adds that if he were THE God, he would know what was going on!) Lampshaded by the character himself when he explains logically why he's come to this conclusion. Rita brings him back to Earth thusly: "You're not a god. This is twelve years of Catholic schooltalking."
Bruce Almighty features a mortal (that's Bruce!) who is granted divine powers for as long he wants. Bruce, being a flawed and limited human, ensures that mistakes are made. The trope is deconstructed since Bruce does not use his powers for any greater jobs than teaching his dog to urinate into a human toilet and advance his reporter career by creating amazing events to report. But by doing even such pathetic things he still manages to make big problems for himself and everyone, and manages to lose his girlfriend because she prefers normal Bruce. So God must take his place back and fix everything in a snap using same powers.
Spider-Man: The Green Goblin/Norman Osborn in the first movie seems to fit this bill. "There are eight million people in this city. And those teeming masses exist for the sole purpose of lifting the few exceptional people onto their shoulders. You, me? We're exceptional."
From Caligula: "I have existed from the morning of the world and I shall exist until the last star falls from the night. Although I have taken the form of Gaius Caligula, I am all men as I am no man and therefore I am a god."
Subverted with his equally insane predecessor and uncle, Tiberius:
Tiberius: It is fate that rules us, Little Boots, not any god. Caligula: You are a god. Tiberius: No, I'm not! Not even when I'm dead. Caligula: Julius Caesar and Augustus Caesar, they are gods. Tiberius: So says the senate, and so the people prefer to believe. Such myths are useless.
A particularly creepy example shows up in Gothika when Dr. Grey discovers the torture dungeon that her late husband used to rape and kill his female victims in. As she watches one of the videotapes that he shot in which he just finished molesting another woman he walks up to the camera, adjusts his tie, and states "It's good to be God. I love you." Near the end, Sheriff Ryan (Doug's friend and accomplice in his rape/molestation/murder of young women) reveals that they shared the sentiment, saying "We were their God."
This idea is poked fun at in Newsies - Joe Pulitzer is obviously full of himself, and pontificates "When I created The World..." (repeated when this speech is interrupted and he asks his assistant where he was. The response? "Creating the world, sir.") But... The World was the name of his newspaper, so he's not quite as full of it as he sounds.
In Almost Famous, rock star Russell Hammond takes too much acid and climbs on a roof at a house party to declare "I am a golden god!" Later, when he has sobered up, he doesn't believe he said it. This is actually in reference to Robert Plant of Led Zeppelin having said the same thing on a hotel balcony.
Deacon Frost's goal in the first Blade movie is to become La Magra, the vampires' Blood God. (no, not that one) He actually does succeed at it, proving immune to silver and far faster and stronger than even Blade, but even a god has to kneel before anti-coagulants.
In the movie Superman II General Zod demands that the president of the United States kneel before him. He agrees to do so in order to save lives. In desperation he utters:
President: Oh God...
General Zod: Zod.
Actually, Zod wasn't implying he was a god. He thought the president had gotten his name wrong.
However, his yellow sun powers have made him believe he has the right to rule the planet.
In The Fourth Kind, a tape recorder is accidentally left running during an Alien Abduction. While the video is reduced to static, the sound remains and the lead alien says (in Sumerian) "I AM *static* GOD!"
Then he stepped on a land mine and ended up being judged by God.
In the climax of Dark Star, Doolittle succeeds at convincing Bomb #20 that its external sensory data is a lie and it itself is the only thing it can be sure exists, in a desperate gambit to make the bomb disregard an inadvertent signal to detonate while still attached to the ship. Unfortunately, the character in question uses this new 'insight' to become a solipsist and eventually decides that, in the absence of anything else having any proof of existence, this means it is, in fact, God. And God said "let there be light"... And there was light...
Sentinel Prime, the Big Bad of Dark of the Moon has a God complex to some degree. He states that on Cybertron, the Primes were gods, while on Earth, the disrespectful humans see them as only machines. This is part of his justification that humanity should be enslaved. When it seems that his plans will succeed, he declares himself Earth's new god.
Johann Schmidt (aka, Red Skull) in Captain America: The First Avenger is shown to have delusions of godhood and according to Dr. Zola, he can't even stop until people say he's a god. It is heavily implied that this stemmed from the serum.
While not specifically stating Godhood, Andrew Detmer in Chronicle implies himself to be an "Apex Predator", giving imagery of a lion not feeling remorse when it eats a gazelle. He then crushes a car, just the drive the point home.