Hmm... let's see...
Dave and Buster's
House of Blues for a concert
Sambucca
shopping at some of the sidewalk shops in Highland Park
eat freebird's on SMU's campus
ice skating and a movie at the galleria or frisco mall
get a friend to have a cookout at their house and then play trivial pursuit or something (this is usually the sort of thing that works best for my GF)
ask her to run a 5K with you some saturday morning. there are activities before and after the big ones that make them pretty fun
rent a movie and buy a bottle of wine. get silly drunk at the house and then terrorize the neighborhood (this again, works surprisingly well for my gf... hahah)
dallas summer musicals
make her a gift basket with off the wall stuff like her own personal scent from bath junkie, a head scratcher, some DVDs you know she hasn't seen but would love... just be sure to play up the sentimental factor
cliche, but still pretty fun: reunion tower's restaurant
grapevine winery tour
JFK memorial
anyhow, that's a start for ideas. I'm sure I have others.