Sorry I don't know how to link to this properly, but go to CNN.com and click on "Watch: Screams for help," an emotional and detailed description of the efforts at rescuing people trapped in flooded New Orleans. [LATER: Look for the "unanswered screams" video here.]
NOTE: This is not a link to a video of people screaming for help. It is a phoned in report from the CNN reporter Jeanne Meserve, who is very articulate. The video shown is of property damage, not of human beings suffering.
UPDATE: I'm watching a lot of news shows tonight, seeing all the people being rescued from rooftops. How many people are out there, stranded and afraid, unrescued as night has fallen? How many people are spending the night on rooftops, waiting for the daylight before they have a chance of being helped? So sad!