In the Spring 2012 Edition of Instructor magazine free resources to celebrate Cinco de Mayo were mentioned. You can find festive math activities, lessons in Mexican history, book readings, a traditional Mexican paper-cutting how-to, and a classroom fiesta. Go to scholastic.com/teachers/unit/cinco-de-mayo-everything-you-need
Secretaría de Educación Pública (México): Viaje por la historia de México
A journey through the history of Mexico with a rich comprehensive survey of Mexican history from Pre-Columbian times to the end of the twentieth century created by the Secretaría de Educación Pública (México). Advanced students. AP recommended.