NOAA has aerial images from the storm area online here:
http://ngs.woc.noaa.gov/katrina/KATRINA0000.HTM
Note that these images have not been rotated to north, so
one might want to compare these images side-by-side with
another map to identify specific landmarks or locations.
Both Google Maps and MSN Virtual Earth offer "before" aerial
or satellite imagery for comparison:
http://virtualearth.msn.com/http://maps.google.com/