If you like that sort of premise, check out 28 Days Later. Falls apart some towards the end, but still a very good movie.With Commentary:
War of the Worlds, 1950's edition: The scene in Denver with the panicking public is rather prophetic.
Damnation Alley. . .if for no other reason than the Landmaster.
The Arrival: aliens causing Global Warming
The Postman: this was one case where I felt the movie did better than the book
The Day After Tomorrow: Good twist.
Carriers: Short run film, but I thouht it was well under-rated. Someone Went in the parking lot and posted Alex Jones Flyers on all the cars.
The Happening : Mother Nature has finally had enough of our crap.
Battle Los Angeles : Even though I think an alien invasion would be a little more in their favor.
Contagion: Possibly the most realistic movie of how a pandemic outbreak would play out. Watch the Food Distribution scene.
World War Z: Running Zombies. . .'nuff said
Special Mentions-
The Crazies: Though the most difficult aspect of a real-life Zombie Apocalypse will be pretending I'm not excited, I don't feel in the Romero-type zombification results. I don't believe in the re-animation of the dead, recently or otherwise. HOWEVER, The Crazies brings forth something I do believe is possible: the drug/virus-modification of the human mind to incite extreme rage, paranoia and sociopathy. We know that both the Soviets and our own gubmint did experiments on this very subject. The Crazies shows an excellent example of a "zombie-type" outbreak where external factors have removed the reasoning parts of the brain and turned people into homocidal killers because a drug or engineered virus was released.
The original Red Dawn - Soviet invasion of the US. 'nuff said.
The Day the War Began - An Australian take on the US' version of Red Dawn. Buncha Aussie kids taking on (IIRC) North Korean invaders.
Zombieland - Mainly because of the kid's list of rules of survival.
I'm leaving out a lot, but these are the highlights.
The Professor