La Fuente is one of several great Mexican restaurants located in the Walker's Point neighborhood on the near south side of town. The quality of the food here is good, and an evening out on their huge outdoor patio in the summer with a couple of margaritas can't be beat.
Aside from the typical fare, I especially recommend the shrimp soup with lime juice.
Don't worry about reservations, but expect a crowd after 6 PM on weekends. They have a designated parking lot for their customers...watch for the signs when you turn onto 5th Street.