iperf - A TCP, UDP, and SCTP network bandwidth measurement tool
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.
JPerf - This project gives a better UI and new functionalities to the initial JPerf 1.
Ping Meter Gadget - Customizable, graphical, semi-transparent ping (latency) meter.
NetStress - NetStress is a user-friendly benchmarking tool that is mostly used by networking professionals to measure the network performance of both wired and wireless connections.
NetCrunch Tools - Our free network tools offer ping scanning, SNMP scanning, port and network service scanning, and more.