Pager Team is a robust, zero-config on-call rotation management system that will let you know when outages occur. It respects shift swaps between two members & won't reschedule leaving you scrambling to get coverage. Works with your existing monitoring system.
Pager Team
I've used both PagerDuty and VictorOps, and the rotation-management aspect of each is far less edit-friendly than Pager Team.
Pros:Locks down on-call so that team changes don't screw with the schedule.
Cons:Unsure!