Be careful when dining at Oyamel - the food is very good, so you might be tempted to keep ordering. Before you know it, you'll have raked up $100 in tacos alone. But go here anyways; it's a great happy hour spot with the deals they offer (half price tacos and margaritas, drinks on sale). Lunch or dinner is equally excellent - they offer free chips and salsa, but the guacamole is worth the price (they make it in front of you). Try their ceviches, all of which are light and fresh. I also like Oyamel for brunch - they offer many of their usual dishes that you can find for lunch or dinner, but add an array of more breakfast-like dishes as well (i.e. huevos rancheros).
Pros: fresh, yummy drinks, flavorful tacos, great brunch
Cons: if you're hungry, prices add up