Freshping is on to a good start. The interface is nice.
Our staff don't want awakened at 3am for a minor website going down so there needs to be:-
Currently using nodeping as it does most of the above but it's a bit "clunky".
Also SMS and voice alerts need to be integrated. I don't want to be setting up and debugging 3rd party services like Twilio. It's an extra layer of billing/support/faultfinding I just don't need.