Since the UN is talking about setting up an international cooperation to help save the Earth from potentially impactual asteroids, I thought I should at least offer up one way that's been suggested to actually divert a dangerous incomer.
Intercepting asteroids to avoid Armageddon
His research is focused on medium-size objects measuring between 100 and 300 meters in length. An asteroid of this size could potentially wipe out entire cities or regions. The scientists have conducted initial laboratory experiments to verify the possibility of deflecting asteroids by impacting them with heavy masses at high speeds -- for instance large space probes. The principle behind the impact is similar to a game of billiards: when one ball hits another, the second changes course. "During impact, not only does the probe transfer its own momentum to the asteroid, there is also the recoil of detached material from the crater, which is ejected against the direction of the impact," describes Schäfer with regard to one of the key test findings. "This recoil effect acts like a turbocharger on the deviation of the asteroid." Tests show that, due to this effect, the overall momentum transferred to the asteroid is up to four times greater than that of the probe alone.
Well, it's a start. At least we have a strategy.