Possessed miners on Mars

First Appearance: John Carpenter's Ghosts of Mars (2001)

A couple of police officers on Mars need to transport a criminal to a remote mining settlement. When they get there it turns out all the miners have been possessed by Martian ghosts. A siege ensues.
This movie is as close as you can get to being a Western as possible with out actually having it set in the old west, using horses or having the heroes fight "injuns." Still wondering when John Carpenter's just going to make that Western he seems to want to make.
Also of note it features a score by John Carpenter (on synthesizer) and a bunch of heavy metal guitarits, including Robin Finck, Steve Vai and Buckethead, and the rest of Anthrax.

Martian

First appearance: War of the Worlds (1953)

As usual Mars decides to kill a bunch of people on Earth. Why? Probably because we're the closest inhabited planet. Or maybe they're just jerks. Either way they do a really good job of wrecking stuff. Will Earth's military or scientists figure out a way to stop this invasion? 

The eventually remade this movie with Tom Cruise as the main character and in a weird twist decided that the martians had buried their war machines all over the surface of the Earth millions of years ago for some reason instead of sending them down in landing craft disguised as meteors like in every other version of the story.

Martian

First appearance: Mars Attacks (1996)

Martians make first contact with Earth. Human's misunderstand why the martians are coming and mayhem ensues. Probably the greatest movie based on a series of collectable cards ever.

Martian saucer design is similar to the one in Earth Vs. the Flying Saucers and the Martians seem to have a similar weakness. 

Martian leader

First appearance: Invaders from Mars (1953)

What happens when a young boy who wants to be a scientist notices a bright light land in the sand pit behind his house? Martians that's what, and they implant things in peoples brains to control them or give them aneurysms. Fortunately the U.S. army is all set to believe the stories of young kids who mention monsters (see Monster Squad). Fortunately everything turns out OK in the end or does it?!