Glenn's list is growing and is the best way I can see for blogger's to contribute to a centralized source that acts as a mainstream-blog-site-of-the-moment, and that's good in a crisis.
Give however you can. (Technorati tags are against my religion, so here's a link to Instapundit. He's got a comprehensive list). I'm with Government Cheese -- go to specific red cross sites, like the Atlanta Area Red Cross, to give specifically for Katrina relief. The link takes you directly to the donation page for Katrina relief.