We just visited the Dallas/Fortworth area this past spring.
I really enjoyed the sixth floor museum (about JFK). Even if you are not into that stuff, I think you will find it interesting. I got this eery felling just know that I was standing in the exact spot where history took place. You can rent an audio tape for a few dollars more. I suggest doing the audio tour. I did, but I found myself stopping the tape because I also wanted to read what was on the signs as well.
My FAVORITE thing to do was visit South Fork Ranch. This is where they filmed the show "Dallas". DH was less then thrilled to do this, But I told him that this was a part of TV History. The tour doesn't take that long, and you get some great background info. After our trip, I was on the hunt for season 1 and 2 of "Dallas" on DVD!
We also visited the stockyards. This is in Fort Worth. It's a lot of shopping and restaurants and bars. Not that exciting, but worth the look at least.
We did some other stuff, but it was in the town called Grapevine. It ws about 20 minutes from Dallas. We went to an Opry there. If you can find one in Dallas I would highly suggest going to it. We saw some really good acts, and even someone that was on American Idol. If you are traveling with kids, they may like it too.
Have Fun!