http://www.livescience.com/technology/destroy_earth_mp.html
I particularly like #4. And iago, theres a Pratchett reference in there, but I can't remember which one. And deadly, the referenced H2G2G, too.
Yeah, too bad it's not a Discworld book, though.
But yup, in Dark Side of the Sun they used a singularity in a box to assassinate (or attempt to.. I forget) somebody. I don't think that really makes sense but eh?
<edit> By the way, he kind of missed the most important and scary one: nanotechnology. #2 sort of alludes to it, but he doesn't even mention nanotechnology. Anyways, read up on that in the Wikipedia article called Grey Goo (http://en.wikipedia.org/wiki/Grey_goo). Grey Goo scares me.