Pingdom

DF Site Monitor

DF Site

http://dfservice.com/site-monitor/index.html.en.htm
Free
http://i.imgur.com/q41Cwmm.png
phpWatch

phpWatch is a free PHP uptime monitoring script that can watch unlimited number of websites and send notifications via e-mail or SMS (for US phones). With an Ajaxed interface, new monitors & notifications can be easily configured. And, once the cron job / scheduled task -that pings the servers in desired time intervals- is set, the script is ready to go. phpWatch also offers an API which lets other applications to query the monitored services, get the statistics and use the notification system for sending SMS and e-mail alerts.

http://sourceforge.net/projects/phpwatch/
Free
http://i.imgur.com/q41Cwmm.png
StatusMon

Monitor services on your server(s) and be alerted when a services fails or is started. Monitor multiple servers Full control over what ports to monitor (on a per server basis) Multiple email address notification options Completely FREE to use Report past uptime history Full admin interface for all settings

http://www.sillydns.com/index.php?title=StatusMon
Free
http://i.imgur.com/q41Cwmm.png
Uptime – Website Uptime Monitoring

Uptime

http://codecanyon.net/item/uptime-website-uptime-monitoring/86651
Free
http://i.imgur.com/q41Cwmm.png