Villa Maria is in every guidebook, and deservedly so. Aside from the excellent Mexican food, the whimsical sayings (in Spanish) on the walls and mariachi band make this a must-visit. Something to watch out for is that they close at 7pm on Sundays.
To start, the margaritas are huge. When they bring it out, you start wondering why they're bringing around a fishbowl before you realize that it's your drink. At about 2 pints (500mL) in size, it'll last you the whole meal. If you want something smaller, remember to ask for it.
Menus are available in English, and most of the food there is suited for sharing. The chef's recommendations are all excellent, but if you can't handle spicy food, make sure to let them know.