Aztec Calendar: Gregorian-to-Aztec date conversion, with Aztec astrological notes.
Early Aztec Understandings: A sixteenth-century account of the religion and history of the Colhua Mexica, or Aztecs.
Historical Science Publishing - Aztec Calendar Handbook: A "technical manual" for the Aztec Calendar and Aztec's perception of God by Dr. Randall C. Jimenez and Richard Graeber.
The Aztec Calendar - Pointer/Homepage: Site breaks down all aspects of the Aztec calendric system