Pingdom is the best. I know a lot of our customers use and trust it. But you can keep using our monitoring tools. I assume that is not forbidden. As many of them you are using as better results you have.
In regards to paid solutions I ma a bit skeptical. I will tell you why, because it has very limited monitoring. Like for example we do monitor all of our services starting from httpd and up to clamvd. So if you are beginner and do not have enough like knowledge simple add you website to the paid service which will do the job. With nagios you can go over much more. You can even monitor your server temperature if you have some more additional devices, but we monitor like 20 services for each of our services. Also you need to manage that nagios would ping those services from several places.
No, not yet.
but it seems my hosting is so reliable…
I believe you need to monitor that everyday. And that doesn’t matter if your web hosting provider good or bad. But in any way that is your decision.
We also have setup SMS alerts which comes to 6 cell phones. In monitoring we also have involved our support team which also got the monitor of Nagios which refreshed every 10 seconds.
Man I believe you have the best monitoring system in the world! 
6 phones!!!
no but member ask what monitoring solutions you have. So I have explained what solutions we have for monitoring our service…I would be glad to hear your solutions as I guess you have more to tell than me ~ServerPoint~?
Yes we have. But I believe OP was interested in the solution as end user not as web hosting provider 
Probably I was too exited 