The zombie thing sounds cool, but how would it work? I mean, you could have a virus that would cause necrosis, but it would kill off the host WAY too fast. Then again, I suppose rabies could do it L4D-style if it mutated, but then you'd only wind up with the basic infected, not the big mutants like tanks, or the weird ones like smokers and witches (I know that doesn't matter, but I thought I'd bring it up for lulz XD). So yeah, zombie apocalypse sounds cool, but if I can state my opinion... gonna have to go with nuclear or meteor impact. Those two are definitely possible. Meteors, well jeez, there's millions of them out there. Nuclear war... well, a friend of mine and I were having a chat a few days back about how the US's economy is going south, and their relations with China are getting more and more strained. He said that it seemed like the back-story storyline from Fallout, and I think it sorta does when you look at it... Ahem, but anyway, zombie apocalypse would probably be the coolest form of apocalypse, if it was possible.