It's called Apophis. It's 390m wide. And it could hit Earth in 31 years time

http://www.guardian.co.uk/space/article/0,14493,1660485,00.html

Scientists call for plans to change asteroid's path.

Developing technology could take decades

In Egyptian myth, Apophis was the ancient spirit of evil and destruction,
a demon that was determined to plunge the world into eternal darkness.

A fitting name, astronomers reasoned, for a menace now hurtling towards Earth
from outerspace. Scientists are monitoring the progress of a 390-metre wide
asteroid discovered last year that is potentially on a collision course with the
planet, and are imploring governments to decide on a strategy for dealing with it.