A Los Angeles institution for a reason. Extremely good food in a fast food atmosphere. They have one of the top Zagat food ratings in LA and you can get lunch for under $5 and a big dinner for under $10. The only problem is you need to remember to bring cash or face the shame of using the in resturant ATM (like I said fast food atmosphere).
Best burrito place ever! Authentic place, if in a somewhat scuzzy area. Their BBQ beef burrito is the best, but for the more adventurous there are more exotic choices (say Tripe or Head). Also the Horchata (a sweet rice milk drink) is absolutely wonderful. This is definately one of my favorite places in Pasadena. Plus it is open incredibly late, a plus if you are a college student.