Is It Down Right Now? - Network & Admin
Ping Meter Gadget - Customizable, graphical, semi-transparent ping (latency) meter.
UPDOWNtoday - UPDOWNTODAY allows you to check whether the website is down or not.
SmokePing - Smokeping is a tool for measuring latency.
IsThisSiteDown.org - Free tool to check whether a site is down just for you, or for everyone.
Open Nettest - Open Nettest is a platform for collecting, processing and visualizing data related QoS and QoE.