This seems to be the best tool we've seen to track individuals who may be unaccounted for following Katrina.

Lycos: Katrina Missing Persons Site http://www.lycos.com/katrina/
With multiple small databases of survivors, we desperately needed one search engine that would search through all of them, and Lycos created one.  The site lists all the databases it searches through. If you're aware of others, please fill out Lycos' form to add them.