Zocalo Restaurant on 10th Street near Piedmont is one of the best and most authentic Mexican restaurants in the city. They also have several tequilas, ranging in price from less than $5 to $60 per shot!
This is not your typical Mexican restaurant. They do not serve tortilla chips on the table, so don't ask! Everything on the menu is good, believe me. I've tried it all. The walls roll up when the weather is nice, giving the place a unique atmosphere.
Favorite Dish: Margaritas, Diez Diez, flan
The other great Mexican restaurant in Atlanta is Zocalo, found right in the middle of Midtown (10th and Piedmont).
Zocalo serves authentic gourmet Mexican, one of the few restaurants I've ever seen do this north of the Rio Grande. The food is delcious, and the neighborhood is one of the few sophisticated urban areas in Atlanta which makes for terrific people-watching. Great food.