Santana's is a small chain, limited to the San Diego area (as far as I know) and is the ultimate in California-style taquerias. You can drive thru or dine in.
It's not quite hole-in-the-wall as all of the locations are really clean and fairly new or newly-renovated, but it has that sort of authentic quality. Their salsa bar is also quite good.
You can get things like horchata, tacos, burritos, plates, and tamales.
Though the star, for me at least, is the California burrito. This thing is a half a pound of heaven. It's a basic burrito, but with guacamole, cheese, and french fries inside. It sounds weird, and it's most certainly unhealthy, but it is delicious.
This is a must for San Diego California/Mexican food.