Given what we know now about New Orleans, the rate of sinking, how the entire landmass is sliding slowly off the continental shelf, I do not believe New Orleans should be rebuilt at all. But hey, rational analysis is not the strongpoint of our species so expect a few trillion to get wasted on New Orleans as it gets rebuilt two or three times over the next 50 years.
If the world is at or near the peak in production of cheap oil, then isn't it clear that there won't be the money for multiple rebuildings of New Orleans?  In fact, it's arguable that there already isn't the money for the combination of 1) multiple tax cuts, 2) an invasion, occupation, and rebuilding of Iraq, and 3) rebuilding of the Gulf coast.
Don't worry, they have already more or less axed one of those, the rebuilding of Iraq.
well, ok, just so long as they don't roll back those tax cuts.

Krusty the clown: "Well, he framed me for armed robbery, but man, I'm aching for that upper-class tax cut."  [votes for Sideshow Bob]

Did I say more or less? Read completely
http://www.guardian.co.uk/Iraq/Story/0,2763,1676911,00.html
I have been following the New Orleans story with the issue of energy lingering in the background.  My conclusion shortly after the hurricane and now is this city is not coming back.  Not in it's previous form and probably nothing more than a shell of itself.  There are too many geological strikes against the region.

Check it out:
http://unplanning.blogspot.com/2005/09/case-against-rebuilding-new-orleans.html