http://www.carloslabs.com/projects/200712B/GroundZero.html
For those curious just how much of their city a nuclear explosion would destroy, this Google Maps mashup will satisfy your morbid curiosity. Choose from a range of explosive power, from the slightly-bigger-than-a-suitcase-nuke destruction of Little Boy (15kt) to the oh-god-the-world's-over impact of an asteroid.