Destroying the Earth is harder than you may have been led to believe.
The Top 10 Ways to Destroy the Earth, which I saw (as did you, no doubt) on metaFilter.

It's a thoughtful list of the ten most feasible plans for removing the planet from existance. Note that this is not a list of how to kill all life on Earth, as "[t]here are far more efficient ways of doing this, many which are available and feasible right now."

They are ranked in order of practicality, where number ten--simply waiting until, through random chance, all of the atoms in the earth spontaenously cease to exist--is the least practical, and number one--push the Earth into the sun--is the most practical.