We all know what the zombie apocalypse might look like. I mean, there are hundreds of movies exploring dozens of possibilities: fast zombies, slow zombies, zombies as an infectious outbreak, zombies where the world has changed and nobody stays dead, stupid zombies, smart zombies... zombies, zombies, zombies.
But there are plenty of other possibilities for a monster apocalypse that I think are... underexplored. Vampire apocalypse, for example. The classic is Richard Matheson's I Am Legend, which spawned at least three movies, including the recent Will Smith version, an older film with the same title, and The Omega Man (featuring Charlton Heston). The treatments differ a little, but the basic dynamics are the same: by night, the vampires hunt humans, and by day the humans hunt vampires.
That's far from the only possibility, though. What if the vampires have taken over because of the hypnotic abilities they're sometimes portrayed as having? What if they can come out in daylight? (In Bram Stoker's book, Dracula could move around just fine in daylight, he just didn't have any powers then and could be killed like a normal man.)
The one I'd really like to see, though, is a werewolf apocalypse. There are tons of possibilities here, and a lot of them depend on the nature of lycanthropy. I can easily picture a scenario, for example, where every full moon there are more of the beasts, and more people dead... but in the days between, you don't know who they are.
What if the infection changes you into a beast permanently? As a human, you'd end up facing off against a world of creatures that were fast, strong, relatively smart, and very hard to kill - oh, and they can follow your scent. Frankly, I'd rather fight vampires.