Use this online Aztec calendar to see what day of the year it is.
The Aztec Calendar: Math and Design http://www.earthmatrix.com/serie02/cuad02-1.htm
An explanation of science in ancient Aztec artwork.
Mesoweb : An Exploration of Mesoamerican Cultures
Subtitled An Exploration of Mesoamerican Cultures, this site is "devoted to ancient Mesoamerica and its cultures: the Olmec, Maya, Aztec, Teotihuacano, Toltec, Mixtec, Zapotec and others" and presents information about an archeological dig and restoration project at Palenque in Chiapas, Mexico. Photo, map, animations, videos (requiring QuickTime), rubbings of Maya sculptures, and an illustrated encyclopedia are available as well as the text of the first Palenque roundtable: a conference on art, iconography, and dynastic history of Palenque. There are related links. A joint venture of the Pre-Columbian Art Research Institute (PARI) and Mexico's Instituto Nacional de Antropologia y Historia (INAH).
Indigenous People.net - Aztecs
This site from Indigenous Peoples Literature, a non-profit resource "for the advancement of all cultures," provides information on Aztec history and culture, with useful links to maps and other images.