As Greg pointed out, nuclear weapons are going to be a major point of discussion over the next few weeks because of the upcoming posture review. However, while most people are aware of nuclear weapons, I think many people have lost the sense of their destructive power, with wild over and underestimations of the strength of nuclear weapons. Fortunately, there is the World Wide Web to help. There are three easy to use resources I like:
The Federation of American Scientists has a wonderful site on all WMDs which unfortunately does not currently have funding for maintenance, but nonetheless still has excellent information.
CDI maintains a database of current world arsenals, grouped by delivery system. It is admittedly imprecise, but fairly clearly illustrates the nuclear world we live in and the level of threat that is out there.
Finally, if you even wondered if there was a nuclear bomb dropped on your city who would survive, then HYDESim, is the site for you. The link will show you the blast radius of an average thermonuclear device detonated in Grant Park, Chicago, but you can play with it to make it fit an area you are familiar with. I find most people greatly overestimate the destructive power of nuclear explosions. What this map doesn't show is nuclear fallout, which would vary wildly based on atmospheric conditions, and blast altitude.