I work for an MSP in Europe and am in charge of pretty much everything technical.
We had a conversation the other day which could be added to what we are currently monitoring.
We had ideas like active SIP trunk connection (status, quality) and log monitoring of SIP trunks at phone systems, Windows account creation (local, domain, group membership monitoring, open files (unusual patterns), processes accessing the webcam (anti-spy) etc.
What do you monitor with your customers?
Info: Some of the ideas above even come from customers