Just bumping an old topic. 2009 DD45 just missed — it is approximately the size of the object which smashed into Siberia in 1908. (whew)
http://neo.jpl.nasa.gov/ca/
http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2009%20DD45;orb=1
http://neo.jpl.nasa.gov/risk/
How close did it come?