NOAA.gov has posted a series of arial photographs of the damage, however the site is not very usable. Here are a couple of shortcuts:

• NOS Data Explorer: This is an interactive map with links to images of Katrina. When you get to the first page, type "Katrina" in the keyword box. You’ll see a bunch of red dots appear over the Gulf Coast. Take your mouse and highlight this area, the map will zoom in. There are tools at the top to use to zoom and move around as well. When you get to a place where you want to see the actual pictures, click on the "Link to Data" button at the top.
• Hurricane Katrina NOAA Images: This page has several zip files of photos that you can download to your computer of areas hit by the hurricane.