On the Texas Gulf coast, Rockport and Galveston have plenty of shrimper fleets, oil rigs, old rattle trap buildings and other sorts of local color. Lafayette, Louisiana is the heart of Cajun country, and I would recommend visiting Breaux Bridge, the Atchafalaya Basin, and if you are really adventurous and want to see some real wetland living, go on down to Golden Meadow and Larose, then head back up the river to New Orleans.
New Orleans is very picturesque, and also very dicey, crime-wise. Be aware, talk to some locals, and don't just assume that walking four blocks away from Bourbon Street will be necessarily safe. If you are planning on doing big camera photography in N.O., I would highly recommend the buddy system. If you are using handheld cameras, be discrete and non-flashy. New Orleans is one of the few places around where getting robbed at gunpoint by a six foot tall transvestite will just generate a yawn from the police officer taking the report.
North of N.O. try the River Road and visit some of the old ante-bellum plantations on the way to St Francisville and Cottonport.