Wikimedia
Wikipedia: Maya Civilization
Extensive information about Maya history and civilization covering a wide range of topics.
Other
Houghton Mifflin: Mayan Mathematics
This site explains the mathematical system of the Mayans. It gives the represenation they used for numbers and how they did addition and subtraction.
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.
Curated OER
Wikipedia: Maya Civilization
Extensive information about Mayan history and civilization with numerous links on additional topics, such as Mayan childhood and music.