Well, it's tough without knowing anything about you, your interests, or the part of town you'll be in.
That said...
The Dallas Museum of Art is hosting an exibition of artifacts from King Tut's tomb that has been getting a lot of notice here. I'd suggest advance tickets if this interests you.
The Nasher Sculpture Garden (next door to the DMA) is always a nice place to spend an hour when the weather is good. I hate art museums myself, but I like this place.