When I was a boy Congress held a series of hearings about the quality of television programming. They were concerned that TV was not living up to its potential to educate people. Television was called a "vast wasteland". Things haven't gotten any better since then. One would think that channels with names like the History Channel, the National Geographic Channel, the Discovery Channel and the Learning Channel would produce shows about the Maya that were well-researched and educational. One would be wrong. These same networks produce shows about the Loch Ness monster, the Roswell flying saucer crash, Atlantis, Bigfoot, Nostradamus and aliens building the Egyptian pyramids. These shows predicted the end of the world on December 21, 2012 and interviewed weird pseudo-scientists about their bizarre apocalyptic theories. The worst of these are the History Channel's horrible programs about the (non-existent) "Mayan Doomsday Prophesy".
The problem with searching for information about the Maya calendar on the internet is that you will find the sites of new-age spiritualists. These psuedo-scholars know almost nothing about the Maya calendar and mix this ignorance with a hodgepodge of other esoteric spiritual beliefs and modern urban legends to invent bizarre pseudo-Mayan calendars and profit from this by writing books about it. An example of this is José Arguelles. José's "Dreamspell calendar" is his own invention, synthesized from Maya and other esoteric cultural traditions and the parts of his calendar that are supposedly Mayan are wrong. Other examples of this are Ian "Xel" Lungold, Dr. Carl Johann Calleman, Terrence McKenna, Marc Smulders and Rohaan Solare.
In science, papers are printed with extensive references in journals and are peer-revued. On the Internet anyone can clip some text from some site and paste it into his. This unattributed, unreferenced information is more or less rumor. Unfortunately it is just as likely to be complete crap as accurate information. They say that if you tell a lie enough times it becomes the truth. This is the situation with the internet and is why it's an abyss of disinformation about the Maya calendar.
Many of the sites you get when you do a search for information about the Maya calendar will be sites that are devoted to promoting the 2012 doomsday hoax.
Even Maya calendar sites that are really about the Maya calendar are superficial and inaccurate. I don't have the time or motivation to try to read and revue all the Maya calendar sites but I cautiously endorse the Wikipedia articles about the Maya Calendar and the Long Count.
When you try to study the Maya calendar and astronomy you will find that the most insidious source of misinformation is books written by established scholars. This is because you know not to believe the psuedo-Mayan fiction of the new-age spiritualists, but you may believe the books of famous scholars of the Maya. Many of these academics are guilty of ignorance, shoddy and careless research and writing. Generally they use the proleptic Gregorian calendar and often the 584,285 Thompson correlation. As Salvo de Meis says in Heliacal phenomena: "...exercise great filtering care in considering the views of ancient and modern writers." Here are a few examples: Cycles of the Sun, Mysteries of the Moon: The Calendar in Mesoamerican Civilization by Vincent H. Malmström is horrible. This book gets almost everything wrong before adding wild unsubstantiated theories. David Stuart's book The Order of Days: The Maya World and the Truth About 2012 contains historical and arithmetically impossible assertions. Can you understand what he says on page 240? Good, because neither can he. Linda Schele and Davie Freidel's books use the Thompson correlation even though she knew it was wrong. She did this in respect to Floyd Lounsbury because he was her mentor and she didn't care if the conversions to western calendars were wrong because her books were written for the general public, not specialists in the field. The calendar conversions in An Illustrated Dictionary of the Gods and Symbols of Ancient Mexico and the Maya by Miller and Taube are wrong and inconsistent. The Ancient Maya by Sharer and Traxler promotes the myth that there is some (non-existent) 13 bak'tun cycle in the Long Count. Then they include an appendix with a big table of conversions from the Long Count to the proleptic Gregorian calendar and advise the reader to use these dates to study Maya astronomical inscriptions using astronomy programs (all of which use the Julian/Gregorian calendar with astronomical dating of negative years). Don't rely on just one book because they are filled with errors.
This doesn't mean that there aren't excellent books about the Maya calendars and astronomy. Here are a few that I recommend:
Aveni, Anthony F. (2001). Skywatchers. Austin: University of Texas Press. ISBN 0-292-70502-6
This is a revised edition of Dr. Aveni's
Mesoamerican archeoastronomy book The Skywatchers of Ancient Mexico. Surprisingly for an astronomer, Aveni did not use astronomical methods for his conversions between the Maya and western calendars, instead inventing a new method for doing this, using tables of decimal numbers. Unfortunately there is some problem with this method and with only a handful of exceptions, all of the calendar dates and astronomical event dates are wrong. He also accepted, without checking them, many dates from other authors who used either the foolish, ficticious Proleptic Gregorian calendar and/or the erroneous 584,285 day Thompson correlation. This could have been checked quite easily using readily available computer programs. For this reason, chapter IV and its appendices should be rewritten. This problem severely compromises an otherwise monumental work of scholarship.
Bricker, Harvey M.; Bricker, Victoria R. (2011). Astronomy in the Maya Codices. Philadelphia: American Philosophical Society. ISBN 978-0-87169-265-8
This excellent book describes the astronomical content of the Maya codices.
Coe, Michael D. (1992). Breaking the Maya Code. London: Thames and Hudson. ISBN 0-500-05061-9
This is a book about how modern scholars
deciphered Mayan writing.
Jones, Christopher (1984). Deciphering Maya Hieroglyphs. The University Museum University of Pennsylvania
This book is particularly valuable for its
description of the glyphs in the secondary series.
Meeus, Jean (1991) Astronomical Algorithms. Second edition with corrections as of August 10, 2009 Richmond: Willman-Bell. ISBN 0-943396-61-1
Astronomical Algorithms is the Bible of astronomical calculations. If you want to write Maya calendar programs you need this book. Astronomical Algorithms is excellent because of its complete list of algorithms with examples.
Tedlock, Barbara (revised edition 1982). Time and the Highland Maya. Albuquerque: University of New Mexico Press. ISBN 13:978-0-8263-1358-4.
This book describes the use of the Calendar Round by Modern Mayan time keapers in Guatemala.
Thompson, J. Eric S. [1971] (1978). Maya Hieroglyphic Writing; An Introduction (Civilization of the American Indian Series, No. 56),
3rd edition, Norman: University of Oklahoma Press. ISBN 0-8061-0958-0.
This is very useful for it's drawings of many versions of calendric
glyphs and chapters about the calendars. Thompson had the Maya calendar deciphered in 1950 thanks to the work of Teeple and others.