Wikipedia is the most concentrated constantly evolving resource on Katrina and her aftermath. They also have a database of live streaming audio and video from the area.
I had a spat of addictively refreshing the well administered NOLA call for help blog
The Hurricane is captured live on video in this stunningly graphic and dramatic video that I’ve only seen on WLBT, Jackson Mississippi’s NBC affiliate.
A good database of Hurricane Katrina related links is at the Online Journalism Review.
Other good blogging and commentary has been seen at AMERICAblog, Crooks and Liars, MediaBistro, and of course Technorati will hook you up with about anything.