This article gives us scenarios that range from the familiar (nuclear war, divine intervention) to the incomprehensible (the Omega Point). In between are somethings that might not have caused you nightmares before, but might now! Link -Thanks, Jon Jason!
I have no idea why i remember that.
http://www.exitmundi.nl/exitmundi.htm
The "divine intervention" one wasn't so much about an actual divine intervention, but about what might happen if religious zealots obtain access to really powerful weaponry.
Hopefully, these weren't listed in order of likelihood, since alien attack was above ecosystem collapse.
You can give me your money and your virgins too.
they have an awesome outlook, although alot of the people are a tiny bit psycho and want us all to drink the proverbial koolaid...
Always scary to think about it going down like that.