ServersCheck is a tool for monitoring, reporting, and alerting on network and systems availability. It can monitor any TCP Port (HTTP, HTTPS, FTP, NNTP, POP3, SMTP, VNC, DNS), check ODBC, Oracle, MySQL databases, trap SNMP values (disk space, free memory, CPU usage), verify content served from a web server and check NT services and process availability. In addition, it also can monitor environmental devices like temperature, humidity, flooding.
http://www.serverscheck.us/monitoringsoftware.asp