IMPORTANT UPDATE, 9/7: There is now a clickable depth map for New Orleans at http://mapper.cctechnol.com.

Here is my discussion of how to use it in combination with Google Maps to check out your house. Also, my Katrina album has some some more sample images. Furtehr UPDATE: the depth map is now searchable by address.

IMPORTANT UPDATE, 9/17: VirtualEarth's Katrina Flyover  has excellent aerial photos searchable by street address. The interface does not work on all browsers. If you have trouble, see my post describing a workaround.

Another IMPORTANT UPDATE, 9/17: Much more detailed instructions for using Google Earth to check on your house are posted HERE.

The best way to check if a New Orleans address is under water is by using Google Earth and the techniques and overlays created by the Google Earth Current Events Community.  Since GE doesn't have their Mac version out yet, I myself can't do it that way.

UPDATE: Here are the promised Google Earth instructions from our hero Shawn:

1) Install Google Earth
a) http://kh.google.com/download/earth/index.html
2) Click the NOAA Overlay Link from Google Earth Community BBS
a) Mississippi Coast - http://earth.google.com/katrina.html
b) http://bbs.keyhole.com/ubb/showthreaded.php/Cat/0/Number/92563/page/3/vc/1
i) Click "Open This Placemark"
ii) Either open file or save to disk and double click.
c) Check the Current Events Board for many more overlays of specific areas.
i) http://bbs.keyhole.com/ubb/postlist.php/Cat/0/Board/currentEvents/page/0
3) Once overlay is open in Google Earth, Enter your full address in the search field in the upper left corner.   That will center the view on your address.

If you can't or don't want to do it that way, here is a shot-cut.

Step 1: Go to Google Maps and enter the address. Click on the button that says "Hybrid" on the upper right. You will get an image with a speech ballon pointing to a thumbtack showing the location of the address on the satellite photo.
[IMPORTANT UPDATE: Bless their hearts, Google Maps has added a "KATRINA" button to New Orleans areas searchs, so they have automated some of the process I descibe here! Yee haw!]

Step 2: Click up and down the vertical ladder-like bar to see the image at various scales until you feel you can find the place on a satellite image.

Step 3: Compare your image to this superimposition of the FEMA flood map on a New Orleans satellite photo, created by the Google Earth Current Events Community. Here is a small version. Click on it for a much bigger picture.

If the address you are checking is fairly centrally located, you can also check your address image against the DigitalGlobe satellite picture of the flooding.

I hope to post some good Google Earth instructions later. I'll be out for several hours, so if you have some, post 'em in the comments until I get back.

OR PERHAPS I'VE BEEN TO OPTIMISTIC: While I was out driving around Pleasantville a little while ago, a reporter on NPR described all of New Orleans as being flooded. Perhaps she was being hyperbolic. But the more important question for those who need to know about specific addresses in New Orleans may be how deep the water and how swift the current; this all combined with information about the rise and fall of the tides.

BY THE WAY: If you get ahold of Before and After pictures of your house, BE SURE TO KEEP COPIES so you can submit them with your homeowners insurance claims, applications for FEMA aid, and other such. It seems to me that providing physical evidence specific to your address would be likely to expedite claims processing.