CMidd - 6:05 am on Mar 17, 2011 (gmt 0)
i use pingdom and monitor us and have been using them for years. They check you homepage once an hour and send you an email.
both free and good.
it's not expensive to create a remote monitoring service LOL. You can create one for less them $100 bucks a month.
5 shared hosting accounts in different part of the world. script to request a page, php mail send. That's it.
you could easily monitor 100,000 site at 1 hit per hour.
the script only check for http response code 200 "less then 1k bytes".