Canadian Museum of History
Canadian Museum of History: Maya Civilization
Lots of information about many facets of the Maya civilization. Covers the history, people, geography, languages, cities, society, cosmology, the calendar, and lots more. Includes a glossary and a timeline.
Wikimedia
Wikipedia: Maya Civilization
Extensive information about Maya history and civilization covering a wide range of topics.
University of St. Andrews (UK)
University of St. Andrews: Mayan Mathematics
After a historical introduction, this site from the University of St. Andrews provides information about the mathematics of the Maya Civilization and shows just how advanced they were.
Other
Mesoamerican Religions
Discusses features of the religious practices of the Maya, Mixtec, Zapotec, and Aztec civilizations.