UPDOWNtoday - UPDOWNTODAY allows you to check whether the website is down or not.
Ping Meter Gadget - Customizable, graphical, semi-transparent ping (latency) meter.
IsThisSiteDown.org - Free tool to check whether a site is down just for you, or for everyone.
Fping (open source) - fping is a program to send ICMP echo probes to network hosts, similar to ping, but much better performing when pinging multiple hosts.
Is it Down? - Is it down can check if a website is down or is it just your PC that can not access it.
Open Nettest - Open Nettest is a platform for collecting, processing and visualizing data related QoS and QoE.