You likely do NOT want the ADO GL site. That lists just the handful of top-class buses. The GL buses are nice, but there are few of them -- for example, from Cancun City to Chetumal there are only two ADO GL buses a day.

The regular ADO site, fairly new, is http://www.ado.com.mx/ado/index.jsp -- it has more comprehensive information, on both GL and the many regular (first class) ADO buses. While I think it is only in Spanish, it is easy to navigate without knowing much or even any Spanish.

--Lan Sluder