I've been trying to work on my definitive guide to CS Tex/Mex and Mexican food.
Category one: You just want something good, aren't trying to have like a semi-nice meal and a margarita. 'B' for breakfast, 'L' for Lunch, D for dinner:
La Familia at Barron and 6 - B/L
Jesse's - B/L
La Carreta - B/L
Yole's - B/L (Yole's does have dinner Tues-Fri, but I've never been there for dinner, no idea what the vibe is like)
Raspas El Payasito - L/D (this is more Mexican than 'texmex', depending on who's working some basic Spanish might be necessary)
La Perla - B/L/D (Same as above regarding English and type of food, also has a meat market near the restaurant if you want to just pick up some fajitas and grill them at home. Best beef fajitas I think I've ever had in B/CS. I also haven't been to the actual restaurant at dinner, so it might have Margarita's I have no idea.)
Note: the above are all places I would consider above 'replacement level' Mexican food. There are a lot of other places that are fine, but if you switched the signs around or something there isn't anything particularly remarkable about them. (ex: Polly's, Coco Loco, Jose's)
Category two: more of a nicer sit down dinner/marg/classic TexMex style. These places are all fine, but I wouldn't consider any of them particularly special.
Lupe Tortilla
Casa Rod
Papa Perez
Chuy's