What are the best ways to stop an asteroid heading for the Earth?

In a 2007 report to congress NASA found that the use of nuclear standoff explosions were 10-100 times more effective then any other alternative considered in the study.

The primary benefit of this approach is the amount of force it exerts on the asteroid. Unlike other techniques that require years to work, this approach would be effective on asteroids mere months away from impact.

This is critically important as our goal for 2020 is to be able to detect 90% of the near earth asteroids. Our current capacities are well below this, and even when implemented the new systems will result in a significant portion of the asteroids remaining undetected. This number increases dramatically if 20-30 years notice is required for the deflection of the asteroid, making the ability to quickly react to an incoming asteroid critical to our survival.