Baja Burrito is a Nashville institution. It is always, always full, the best indicator of good food. The menu is basic: burritos, tacos, taco salad, chips and salsa. From there, though, you can customize and get what you want exactly as you want it -- flour, spinach or wheat tortilla, chicken, beef, black or pinto beans, rice, all the standard taco/burrito toppings. Everything's fresh, the folks on the "line" aren't stingy with the fillings, and (an important point many small restaurants miss) it is consistent.
The self-serve salsa bar usually has four different choices; my favorite is the sweet pineapple salsa, but they're all good and always fresh. Sodas are also self-serve with free refills.
Seating is tight, and the restaurant is usually pretty loud. Outdoor seating helps with the crowd but not the noise (it's right next to Thompson Lane).