This is my favorite place for tacos in Phoenix, and now that I've moved away, I really, really miss it!
For just $5 you can get 3 tacos of your choice -- tasty and filling! My husband can eat all 3, but I barely make it through 2. The best part is that they use cabbage instead of lettuce, so it makes the whole taco less soggy and more crunchy (though it's made on a soft tortilla).
The ONLY downside is that they accept cash only (but they do have an ATM machine inside).
I'm a casual girl from the NW, so if you're looking for a casual locale, cheap but good tacos, homemade smoothies, and a beer, head over to Two Hippies. Best in town!