Blackwater USA security firm, notorious for when several of its men were killed and their corpses displayed in Fallujah Iraq, benefitted and profited greatly from the Katrina disaster in New Orleans, to the tune of over $30 million. Blackwater is one major example of private companies which have reaped huge contracts from the American government for performing actions which should have been the responsibility of the government but have been offloaded to the private sector at huge costs. Of course Blackwater in addition to New Orleans has also provided private paramilitary or mercenary sevice on behalf of the US in Iraq for which its main purpose is for.
Blackwater is experiencing large growth because of the frequency with which its services have been called upon.
In the Black (water) provides some background about this company and its operation in New Orleans.

An extract: "We saw the costs, in terms of accountability and dollars, for this practice in Iraq, and now we are seeing it in New Orleans," says Illinois Democrat Jan Schakowsky, who has been one of Blackwater's few critics in Congress. "They have again given a sweetheart contract--without an open bidding process--to a company with close ties to the Administration."