Edit: out of business, declined in quality.
Try MAIZE in Campustown for the best Mexican.
What I ordered: Steak Tacos - best tortillas I've found in the area- fresh, moist, pliable and flavorful. The toppings were fresh and the portions generous. Three different kinds of salsas are kept in a fridge near the pickup window- which means the owners are concerned and knowledgeable about food safety.
Bonus: the restaurant was spotless- as was the bathroom- always a good sign!
Edit: Returned again. This time ordering a ribeye sope and enchilada combo plate with rice and beans. The sopes are good and the rice was moist and the beans flavorful. I would pass on the enchilada, or order it with a different sauce. Everything benefits from sprinkled cilantro and a squeeze of the just sliced lime provided. I asked the woman behind the counter- the cheese is imported and unfortunately, because I'm pregnant had to pass on it. My husband said it was good- it looked like queso fresco. It looks like they use mexican "Crema"- not sour cream- also a good sign (again, imported and had to pass on it, but my husband said it was good).
This is a solid taqueria- casual and cheap food. You won't find gourmet Mexican food, like mole, and it's not as good as you'll find in Chicago, but for C-U- this is as good as it gets. MUCH better than El Charro or the Dos Reales that people seem to like- for their nachos and margaritas...