Server is down notification email plug-in

Hi,
I was wondering if there was a plugin that tells me that my server has gone down. At the moment I have a vBulletin forum which sends me an email about errors when some tries to access my site when the server is down and I was wondering if there were something similar for wordpress.

I intend on removing my forum soon but when I do I feel I will have no emails telling me when my site is down.

Thanks