There are a million things to do! Incredible shopping, fabulous restaurants, a couple of fun lakes, if outdoors is your thing. Do the touristy thing: see the infamous grassy knoll and the Kennedy Museum. Sounds corny, but it really IS interesting.
The Dallas World Aquarium is wonderful
Dallas World Aquarium
Tons of special events, festivals, art shows, etc. here all summer long. They are in the Friday Guide in the Dallas Morning News or even better, the Dallas Observer (free "alternative paper).