If you are looking to monitor your servers and provide a way of customers contacting you during times of emergency and you don't want to pay the high prices per server charged by some of the monitor sites take a look at NOC Status (http://nocstatus.net)

You can monitor multiple ports on multiple servers for one low monthly cost $9.95 per month.

The application is hosted on NOCStatus' servers and provides:

An 'Active Alert' button that your customers can use to report a problem - when active a customer can click it to send an email to your designated account

Server Alert - every 20 minutes NOC Status checks whether it can connect to the services you define on each of your servers, if any are reported down it fires off an email to your alert address with the server name and port reported down.

Announcements - where you can add information to keep your customers up to date on what is happening

Server Status - A graphical display of your server status, for any amount of ports/servers you wish

Admin Control - where you can add announcements, define the ports to be monitored, define 'groups' of servers (such as hosting, dns, database, etc) and add the servers to be monitored

You can save hundreds of dollars a month, take a look at the details here (http://nocstatus.net/services.php)

If you have any questions please forward them directly to the NOC Status sales team sales at nocstatus.net

What advantages does this have over a Nagios monitoring system?

Many thanks,
Matt

It's not run on your servers or network so is an independent display of your server status and so not affected if your network goes down or the server goes down.

It also allows your visitors to send a report to you if a server/service is down and allows you to post announcements to your customers even when your network/server is down.