nmon - This systems administrator, tuner, benchmark tool gives you a huge amount of important performance...
iperf - A TCP, UDP, and SCTP network bandwidth measurement tool
iftop - iftop does for network usage what top(1) does for CPU usage.
JPerf - This project gives a better UI and new functionalities to the initial JPerf 1.
vtop - vtop is a graphical command-line tool that uses unicode braille to chart CPU and memory usage.
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.