The scale of destruction from Katrina is simply staggering. The Red Cross, and other good organizations could use your help. I do wonder if Pompeii isn’t a better analogy than others being brought up, such as the Indian Ocean Tsunami or Hiroshima.
As an aside, I expect there will be fake charity sites set up, and email campaigns to try to draw you to those sites. Use your favorite search engine, or a bookmark, to find the organizations you’d like to contribute to.