Nuclear War - Not quite as popular as it was in the 60s, 70s and 80s, but still oozing with potential. With the number of countries getting their corrupt misguided hands on nuclear weapons increasing, the number of barking mad tyrants with their finger on the button is similarly increasing.
Fortunately, there is little to be gained from triggering a nuclear holocaust. Even the most ardent megalomaniac seems to have come to this conclusion. Well maybe not in North Korea, but generally it is accepted as a bad idea. Even Ronald Reagan managed to refrain from getting over excited and breaking out the big boy fireworks.
Plague - With the amount of experimentation that goes on with existing viruses, this is not beyond the realms of possibility. I just hope that if it is a disease that puts an end to mankind, that it is not some form of wasting disease. I would hate to see the fat knackers having the last laugh as we all pop our clogs before them. I can just imagine the last death throes of mankind taking the form of large slow moving pie eaters, gulping down their last bargain buckets before nose diving into what remains of the pot holed tarmac. Much the same as the demise of the last of the dinosaurs.
Giant Meteor Strike - The likelihood of this happening is not as great as the scientists would have us believe. The reason being that we now have at our disposal the means necessary to repulse such a threat. A huge stockpile of nuclear weapons and hoards of spotty schoolboys that have honed their shooting skills on a variety of video games.
Environmental Breakdown - The way we are working our way through the earth's supplies of coal, oil and gas, it won't be long before we actually run out of pollutants. Thus bringing this threat to an end.
As for global warming, it could be a blessing in disguise, ridding us of the spam smelling ginger mutants. Also crops would change for the better. Which do you prefer, sprouts, cabbage and swede or pineapples, mangoes and bananas?
So how will the world end? What will bring down the final curtain on the existence of the human race? As usual, I've pondered long and hard on this dilemma and realised that the answer is blatantly obvious. Don't look to the skies, look to the chavs, the trailer trash, Jeremy Kyle guests and other undesirables that act as a cancer upon our society. They continuously take, often by illegal means, without ever giving back. They also multiply at an alarming rate, without having the necessary means to support their vile offspring. Consequently, the cancer will continue to grow until society is no longer able to support their perceived needs. The undesired element will then turn upon it's hosts. Their numbers will be by this time greater than ours, hence our demise. However, if our days are numbered, then likewise so are theirs. The parasite needs a host to survive.
Obviously, it doesn't have to end this way. We could always pre-empt and strike first.