I'm currently leaning towards the theory that the world will end via a giant volcanic explosion. I once saw a special on NOVA about how there is a huge amount of lava building up under the surface of the earth, which very well could be released in the next few hundred years. This kind of seismic explosion, which I believe would be equivilant to thousands of volcanoes going off at the same time, would probably incinerate the entire surface of the earth, and might even cause the earth's structure to decay. Whatever the case, the earth will be destroyed.
Personally, I think this is much more likely than an asteroid collision, both scientifically and spiritualy. Scientifically, because there still is little likelyhood that an asteroid will hit the earth in any reasonable period of time. Spiritually, because since I don't believe the earth will be destroyed by a flood again, a fire related destruction makes a lot more sense.
(Note: like the others, I'm not trying to start a discussion about theology - this is just my personal opinion and doesn't need to be turned into a huge debate with multiple sides. :P )
