I'm partial to Mercado Juarez. Great food. Great fresh tortillas. Great salsa. Great price. Any other good local Mexican restaurants anyone would like to share?
Try Primo's in dowtown Dallas. They have pretty good specials during the week, and the house Margarita is pretty good, and super cheap on tuesdays (?).
Desperado's off of Greenville is pretty good to. Great service at least.
The best place I've found is Superior Grill, but that's in Shreveport.
For a a good authentic Mexican style meal, you can try La Michoacana Meat Market. They are all over the place in Dallas and the surrounding areas. They have awesome food, for a very good deal. They also make fresh tortilla's, and have a taquer?a in the front that has some of the best barbacoa I have ever had...
If you're looking for a nice sit down atmosphere el portrillo (sp?) is awesome. It's located in Rockwall at the harbor. They also have salsa classes I hear... For more casual mexican food, try the area white rock lake. There are lots of local hole in the wall dining options.