There are some questions about the Red Cross, but I'm not educated enough about them to really expound. The United Way is also pretty shady with the way they handle donations - after the scandals they've had, I wouldn't donate to them.
Even so, I've donated to the Red Cross a few times via:
http://www.tvland.com/familytable/familyday/index.jhtml
I've been doing that since I can't actually spend any of my own money - my bank is in New Orleans.
Louisiana Disaster Recovery Foundation:
http://louisianahelp.org/
Keeping it hip-hop, David Banner's "Heal the Hood":
http://healthehood.com/
^ The advantage of these two are that they ARE in the area and can reach people immediately. David Banner's is on point because it isn't just focusing on helping people in Louisiana - Mississippi got hit pretty hard, if you'll recall.
There are lots of charitable organizations out there working hard.
http://www.hurricanehousing.org/
http://www.networkforgood.org/topics/animal_environ/hurricanes/ - This is a good umbrella of different charities.
I hear Americares is also good.