The weather channel had some good information on shelters and there were a couple of more links within the article.
http://www.weather.com/activities/ho..._shelters.html T
They also had a segment in their "weatherproof" series where they tested a shelter from F-5 storm shelters. That one seemed to work quite nicely during their test, and I know there are many other types as well.
I just wonder if they will let you install one if you decide to build a home, or if they would let you put one in an existing home (most likely in the garage?)....