I am looking for some kind of auatomated system where I can enter a list of domain names and the nameservers that they should be using.

Then, once per day, the system checks to see if the domain name is still using the correct nameservers. If not, then an email is sent to me, so we can check it out.

The idea is that we sometimes don't know about a customer changing their domain to point to another company, until after they have moved and stopped payment. Or perhaps their domain has expired and the nameservers changed to a parking page, etc..

With a "resolver check" we could pro-actively contact the customer to find out what is the status, etc..

Anyone know of such a service?

My guess is that with a little tweaking you could probably get the chkcpaccts script to work located at http://www.cplicensing.net/scripts.php#chkcpaccts

Plesk Power Tools can do this (sure, if you use Plesk :)).