(If this link doesn't work, go to http://www.bostonglobe.com and open their "Ideas" section in the top blue bar.)
This is an interesting graphic-article from today's Boston Globe, which discusses all the current ideas for how to stop-a-killer-asteroid.
This is an 2008 article, discussing how the UN has been urged to coordinate various countries' defenses against an incoming killer asteroid.
This is also an older but interesting article, DEEP IMPACT: RACE TO TAG KILLER ASTEROID
So which defensive strategy against an incoming killer-asteroid do you favor?