WebCron - Arrange to do tasks at set hours by looking for a page on your website. - http://www.webcron.org/
Hosted Cron - This site can help you with the automation that programs need most, a scheduling system that automatically runs the maintenance and cleanup scripts when you need them run, 24 hours a day, 7 days a week, 365 days a year. - http://hostedcron.com
Change Detection - Service that notifies visitors about web page changes. - http://changedetection.com/
ChangeDetect - Service that saves favorite web pages, monitors content, and sends an automatic email notification when a web page change is detected. - http://www.changedetect.com/