Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.

Ping Meter Gadget - Customizable, graphical, semi-transparent ping (latency) meter.

Winsock Packet Editor - WPE Pro is a packet editor.

PingDoctor - PingDoctor is software that is considered to be the most powerful and easiest to use network route analyzer.

packeth - packeth is GUI and CLI packet generator tool for ethernet.

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.