Thanks, Christie. If you are going to be in Dallas during State Fair time, you must go. It is the largest (of course) and along with the special events (musical, specialty acts, evening parade & fireworks); you have the Women's Museum (affiliated with the Smithsonian), African-American Museum, Science Museum with IMAX Theater, etc. You can see most of it in a long day. You can spend a couple of days in Austin (LBJ Library, daytrip to Hill Country for LBJ ranch, German influence in Gruene & Fredericksburg); San Antonio can fill up 2-3 days (mission tours--if there on Sunday, go to Mariachi Mass at Mission San Jose; Alamo; Riverwalk; Sea World; Fiesta Texas; HemisFair/La Villita/Boat Ride; etc.)
Houston would be NASA (about 30 minutes south off I-45 and NASA Road 1), Galveston (another 45 minutes south), Alley Theater, new baseball field.