Carolina's is a great lunch spot that is the closest thing Phoenix has to an LA-style tacqueria - hole in the wall location, minimal decor, iffy neighborhood and great Mexican food. Pretty much everything I've had there is great, though a friend of mine swears by their enchiladas.
It gets packed around noon and stays that way until 1:15 or so and my favorite time to go there is around 2 to cram my face until 3 and pass out at my desk until 6.