(Katrina sidenote: Apparently and not surprisingly, the Red Cross site is bogged down - I've only been able to get on sporadically, maybe the rest of you have had better luck.
Other options: if yr a God-fearing type, or a God-appreciating type, or a whatever-type, try your religious organization. Mine, anyways, seems easier to access. I can't speak for any other institutions, cynics, but I'm gonna rep us liberal Lutherans and tell you that this initial $$$ isn't going to missionary work. Funds are being used for travel for disaster response volunteers, food and water, chainsaws, medical supplies and all that other stuff people desparately need.
Again, not pimping the religion thing. If above isn't yr bag, I've accessed Network for Good and FEMA with ease, too.
It seems the most obvious and neccessary help is cold, hard bank. Send a few bucks. I have a feeling Houston might need some extra funds as well, so consider giving to Texas/Arkansas/Missouri chapters if possible. Houston has opened a local phone bank and have a "donate" button on their website that appears to be working.
Anyways, words honestly fail me, which is very rare. I got an email this morning that the family of a friend-of-a-friend rode it through in their Bay of St. Louis/ Gulfport attics, they lost the family's parakeet but otherwise casualties are low. Their homes, obviously, are destroyed. The wedding of friends so carefully planned in NOLA for November obviously won't happen. But you know- the parakeet and the wedding? Such small sacrifices.)