Back in 1980 the USA and Soviets had enough nuclear bombs to completely destroy the world 200 times. With better weapon technology and more countries able to purchase it the chance of a deadly nuclear war increases every day.
There can always be comets that struck our earth which can not be stopped. A big comet could have the same effects as the super Volcano. Plus if the impact is strong enough it could catapult our earth out of it's current orbit leading to dramatic climate changes.
The last but most interesting thing if you ask me is going to earth's definite death. The Sun will have burned all energy in around 50 billion years. When that happens the sun will collapse and transform itself into a red dwarf. With the transform a giant gas cloud of incredible heat will start moving radial around the sun. A few years later the earth will be covered in that cloud resulting in a death of all life. This gas cloud then explodes resulting in a compression of the sun into a neutron star. The sun's gravity will increase and make the earth collapse with the sun. Perhaps, scientists are unsure, the sun will then transform into a black hole. The black hole has a that high gravity that the earth will then vanish in it. That's our end . Not 2012.
Interesting: Black hole - Wikipedia, the free encyclopedia