Current schedules [1]
Past schedules [2]
MMT via MMTO [3]: In the case of a discrepancy, this MMTO schedule takes precedence over the schedules linked above.
VATT [4]: Alternative page
Links
[1] http://james.as.arizona.edu/~psmith/schedules/schedules.html
[2] http://james.as.arizona.edu/~psmith/schedules/oldschedules.html
[3] http://www.mmto.org/schedules/
[4] http://vaticanobservatory.org/VATT/index.php?option=com_content&view=article&id=73&Itemid=67