Contrary to popular belief, Burritos, Fajitas, Hard Tacos and Flour Tortillas ARE authentic Mexican foods. They are just variations. Other traditional foods from Mexico are
Quesadillas,
Chilaquiles(good for hangovers),
Flan,
Barbacoa,
Guacamole,
Pozole,
Menudo,
Nopales,
Chiles en Nogada,
Tortas Ahogadas,
Chocolate,
Tamales,
Jericallas, etc. etc. etc.
Even today, people are inventing new foods by combining old and new ingredients, for example, the "Vampiro", a food that comes from the northern states and is made of a tostada (a "hard" tortilla, fried in maiz oil) with cheese, chorizo and other ingredients on top of it.
As a side note - Taco Bell should never be called real Mexican food - it is the equivalent of calling Domino's Pizza real Italian Pizza.