If you're after Tex-Mex, personally I don't think any are better than Pappasito's Cantina (713.468.1913). Great food. There is one off I-10 just before Beltway 8 in west Houston. Address is 10409 Katy Freeway (=I-10). The address for Goode Company BBQ (713-464-1901) is 8911 Katy Freeway. I don't think you could go wrong with either of these restuarants although Goode Company is sometimes hit or miss. The Swinging Door is probably better but farther out of your way since it's in Richmond, 20 minutes south of I-10.
But if you're in the mood for a nice juicy steak, try the Taste of Texas, at 10505 Katy Freeway. Great steaks! But be sure to bring plenty of $$$, if you know what I mean.
If you get hungry before you get to Houston, there is a fine Caujan resturant in Lafayette, La. called PreJean's. It's on the north side of town about 5 minutes up I-49, I believe, at 3480 I-49 North ((337) 896-3247).
Texas is a big state and it's a long way to El Paso with many wide open spaces in between. How far are you planning on going?
Reviews:
http://www.b4-u-eat.com/houston/restaurants/reviews/rsv0363.asp
http://www.b4-u-eat.com/houston/restaurants/reviews/rsv1235.asp