Most of this is obviously silly such that anyone with common sense can be reassured.
A rogue planet? Ya, we generally can see those things coming. Galactic alignment? Maybe getting the sun and the galactic center adds minutely to the tug on the Earth, but I don't see how the galactic equator adds anything to that force, and if that doesn't add anything then this is a non-issue because we put the sun between us and the galactic center on a pretty regular basis.
The one that always gives me pause is the stuff with solar storms, the magnetosphere, and pole shifts. Magnetic north does flip periodically and there's been some research into the relation of this process to past extinctions. The concern from doomsday types is that this will interfere with our magnetosphere and let in radiation from the sun. Given worries about high points in solar cycles, that does give you pause.
Let me be clear - this has been thoroughly debunked - my blog title was meant as a joke. I am sleeping fine as December 21st actually approaches. But I've always found this one interesting because it's the one prediction that I at least couldn't rely on my own common sense to dismiss.
Actually the most plausible thing that could happen tomorrow, as far as I'm concerned, is that aliens who visited the Mayans will come back. It's a long shot to be sure, but it seems considerably more reasonable to think that intelligent alien life exists in the galaxy and has visited us and has communicated their intentions with us than that a rogue planet is hurdling towards us or moving into galactic alignment does something special. All you need to make an alien visitation plausible is evolutionary biology and a few weak assumptions about the consistency of social science across intelligent life forms.
Proving it actually has or will happen is a different issue entirely, of course.
This is what separates the Sagans of the world from the von Danikens of the world. My preference is to actually be a Sagan that enjoys listening to the von Danikens on the History Channel as a sort of escapism.
Anyway, just a thought I had. Treat this as an open thread on the impending apocalypse.