Robert Frost speculated about the world ending in fire or in ice. Which do you think is likely to end us all: meteorite, global warming, nuclear weapons, zombies, or the superflu?
My idea of the end of the world involves the lack of Darwinist tendencies in today's Western society with an added dose of genetic manipulation in the wrong direction. We basically, genetically, kill ourselves out of existence.
Of course, unstable cores, black holes, weird science experiments at a secret lab that let in another dimension into this one...all are perfectly good ways too go too. I'm also partial to predators stronger than humans or the whole Armageddon thing. I can totally see a nuke going off near ancient Mageddon (from which the name comes!) in the Middle East starting a series of nuclear attacks and the worst fears of the Cold War come to realization. Better make those bomb shelters!