ServerSuit - ServerSuit is a browser based program that enables remote Linux administration, monitoring, website hosting, and server setup automation.
Is It Down Right Now? - Network & Admin
RedGate SQL Monitor - SQL Monitor helps you and your team find issues – before they become problems
Site Down - Site down outage and downtime reports from SiteDown.co
Nagios - Complete monitoring and alerting for servers, switches, applications, and services
IsThisSiteDown.org - Free tool to check whether a site is down just for you, or for everyone.