There are many website monitoring services. But I feel this 100pulse.com has many best features among in FREE services..
  • Two website credit free for life time monitor and save 48USD/year
  • Easy way to detect your web site outages quicker and more effectively
  • Cheapest monitoring Service
  • You can monitor site uptime downtime with 5 min interval
  • Free Instant alert when ever your site goes down
  • No software installation needed
  • Free Periodical Reports depends on user selection
  • Easy way to analyze web site performance through graphs and data
  • Test your website availability, Find your site IP address, Find your server location..