If you’re looking for a free and customizable uptime monitor, you can easily tweak a Google Docs account to do the dirty work for you.
Over at Digital Inspiration they share a great tutorial and bit of code for turning a Google Docs spreadsheet into a monitoring service. All you need is a Google account and a copy of their free spreadsheet to enjoy minute-by-minute monitoring with email alerts. Hit up the link below to read how to set it up and get a copy of the monitoring script.
Monitor Your Web Site’s Uptime with Google Docs [Digital Inspiration]