Wikimedia
Wikipedia: Aztec
An encyclopedia article from Wikipedia on the Aztecs discusses the legend of how they first appeared, their culture, human sacrifice, and the end of the empire.
National Endowment for the Humanities
Neh: Edsit Ement: The Aztecs Mighty Warriors of Mexico
Unit plan to teach about the Aztec civilization. Includes websites, worksheets, activities, and extending the lesson.
Yale University
Yale New Haven Teachers Institute: The Aztecs: A Pre Columbian History
This site contains several lesson plans, a teacher bibliography, a student reading list, and a large amount of background information on the Aztecs.