I live in San Diego and eat fish tacos all the time. Nothing like a fish taco and and ice cold Pacifico. Ralph Rubio has a chain of taco shops that sell fish tacos and he's done quite well with his business. His original recipe came from Ensenada. It uses beer battered fish, a white sauce and a salsa. The white sauce recipe is pretty simple:
1/2 cup mayonnaise
1/2 cup plain yogurt
Topped with the salsa and shredded cabbage and you're good to go. Don't forget the Cerveza.