I'm not an expert on the southeast, but I pulled some ideas off the web, along with what I know about the southwest and came up with the following list of possibles, although I'm not really sure what you're interested in, so I tried to include a variety. I also suggest you pull up each state's tourism site (they ALL have one) and you can see more information on these suggestions plus get other ideas if these don't work for you.

Florida:
-Gulf Coast kayaking -- overnights, dinner cruises, Manatee cruises, etc.

Louisiana:
-Plantation house tours along the Mississippi River
-See the old U.S. Mint
-cultural museums in Burnside, Alexandria and Shreveport
-Tabasco factory tour (New Iberia)
-ride a Mississippi paddlewheeler
-visit the Abita Brewing Company in Abita Springs
-take a heritage tour in Baton Rouge
-Acadia tours in Crowley -- Cajun country and culture -- listen to some Zydeco music!

Texas:
-Six Flags in Arlington
-Schlitterbahn world-class waterpark (New Braunfels)
-LBJ Space Center (Houston)
-Mesquite Championship Rodeo (Fri/Sat nights)
-Panhandle/Plains Historical Museum (Canyon, Texas)
-LBJ Ranch/Presidential Library
-San Antonio; Riverwalk, the Alamo
-Big Bend National Park
-West Texas ghost towns
-go for a horseback ride in the Hill Country (Austin)

New Mexico:
-vist the aliens at Roswell
-Carlsbad Caverns
-Lincoln, NM (old west, Billy the Kid stuff)
-Capitan, NM -- see Smokey the Bear's Grave
-horse races at Ruidoso Downs
-White Sands National Monument
-Pancho Villa museum at Columbus, NM
-Gila Cliff Dwellings, Silver City

Arizona:
-Chiricahua Natl Monument
-Shady Dell Trailer Park Motel (Bisbee)
-Lavender Pit Mine Tour (Bisbee)
-Tombstone, AZ
-Kartchner Caverns State Park (Benson)
-Tumacacori Mission ruins (near Tubac)
-Mission San Xavier del Bac (Tucson)
-Arizona Historical Society Museum (Tucson)
-Las Pocas Cosas (Mexican food in downtown Tucson, don't miss it)
-Old Tucson Movie Studios
-Arizona Sonora Desert Museum (Tucson)
-Kitt Peak Observatory (west of Tucson), daytime tours of the big telescopes and the McMath Solar Telescope.
-Yuma Territorial Prison (Yuma)
-Phoenix -- call Bob for directions to the best barbecue in Arizona (Thee Pitts Again)
-Phoenix -- the Pioneer Arizona Living History Museum
-Diamondbacks baseball? (Phoenix) (or Houston Astros, etc.)

Nevada:
-Laughlin -- out of the way, but a fun day with jet ski rentals on the Colorado River and gambling for Mom and Dad. Dinner at the Gourmet Room at Laughlin's Riverside, reservations req'd, worth the splurge!

California:
-Mission Bay water sports
-San Diego Zoo/Balboa Park Museums
-San Diego Wild Animal Park (more natural settings for the animals)
-Maritime Museum (on the Bay downtown)
-dinner at Vincenzo's (my favorite Italian place)
-fish tacos at Rubios (3 million San Diego locations)
-Sea World, San Diego
-drive out to Point Loma and the Cabrillo National Monument (SR209, I think).

And of course the main Los Angeles attractions will all be there for you as well.