Total annihilation wise would it not be easier and more effective to work form the inside I'm sure there is something in the current scope of technology that could wreck the core, jiggle the plate tectonics, or heck even set off the super volcano that makes up Yellowstone National Park. The volcano itself would put enough ash into the air to block most of the planet from getting heat so it would be a bit of a slow painful death, but mix that with lets say kicking nuke plants into meltdown and the combined mix of ash and radiation would most likely render the planet void of life, then to destroy the planet it's self wait for the several million years for the sun to go red giant.
