To bounce a few ideas your way...
Obvious: Voodoo, Hoodoo (There's a difference, check it out online, and maybe watch the movie "The Skeleton Key"), Zombies
Slightly less obvious: Weregators, Swamp Monsters, Corrupted water and earth elementals
Obscure: New Orleans has a LOT of history, including ties to Piracy and the Slave trade. There are hideyholes and little bits of history tucked into the landscape, and there have GOT to be ghosts aplenty with secrets to share in Dresdenverse New Orleans.
Hope this helps out.