ITA has schedules and availability and covers many - but not all - airlines.

If you just want a timetable check out mine: http://www.wandr.me/Tools/Flight_Timetable.aspx. Registration required, but it is free. The data looks something like this:


The most notable difference between the two - other than that the timetable is a schedule only and does not reflect fares nor inventory - is that the timetable also includes Southwest on the schedule.