I'm in Texas and some of my favorites are:

Taco Cabana - way better than taco bell, fresh salsa bar, they even serve fajita's and margaritas

Taco Bueno - another better than average tex-mex favorite

Whataburger - where else can you get a Jalepeno Burger on the go. Also some great fresh made breakfast taquitos (eggs and bacon in a tortilla) served from 11pm to 11am; perfect for a late night bite or a great start to the day.