I travel to Vegas for business regularly, and my favorite stop for Mexican food is Viva Mercardos. Note that the current address listed here is incorrect. The food and service is top-notch. Make sure you get the "torridos" with your chips and salsa...both are no-charge. Their chorizo burrito is the best I've found...anywhere. I do wish they would open-up a location in Orange County; but then again, I'd have to buy new (larger) clothes if they did.