How will the world end in the immediate future? Slate has a both serious and fun look at this question, allowing users to suggest up to 5 of 144 possible problems that could bring about the end of America and/or the world. These include alien invasion, a swine flu epidemic, and Vermont achieving independence, among many other options.
The application focuses primarily on the United States and its demise, but many problems you could throw into your chosen apocalypse would impact the entire world (e.g. asteroid collision).
I chose Alien Invasion, 2012, Obesity, Cell Phones, and Grey Goo as the most likely causes of the end of the world.
What nightmare scenario do you choose?