There is a place on Harry Hines just east of UTSW (beyond Exchange Park) called Amigos. It is right past the hospital where Harry Hines starts to get scary, so you'll think you want to avoid it, but it is really good mexican food.
Also, there is a place called Grandpa Tony's that has the best Chille Relleno near that area as well. I forget how to get there, now.