I am gratified to see how hard it is to load the Red Cross site, since it must mean that they are overwhelmed with folks who want to help. While their bandwidth is too taxed to handle your contribution, you might think about giving to Modest Needs.
Their general mission is to stop the cycle of poverty before it starts by helping out folks who are basically solvent, but suddenly find themselves in serious danger without a financial leg-up. They function as a stop-gap measure for the huge demographic who have real problems, but whom the government and most aid groups consider "not bad off enough."
In the case of the Katrina victims, they are trying to raise money to help people who, for example, might have just enough insurance to render them ineligible for help from other charitable organizations for things like food and clothing.
Then, when things slow down at the Red Cross, you could maybe give them a little, too.