On the off-chance you haven’t seen this elsewhere, Glenn Reynolds has a master list of charities and relief agencies that are helping the victims of Hurricane Katrina, if you would like to donate.
As a side note, I’ve been told that, when giving to an organization like the American Red Cross, it’s often better to make the donation out to their “National Disaster Relief Fund” rather than the “Hurricane 2005 Relief,” simply because ARC is required to spend the latter fund entirely on hurricanes, and if they get an overflow of donations for Katrina—as seems possible—they can’t use the surplus for other, lesser-noticed disasters. Usually these organizations know best where to spend their funds, so I prefer to give them the flexibility, although obviously any sort of donation helps a great deal.