1:  siege - An HTTP/HTTPS stress load tester

    2:  abcde - A better CD encoder

    3:  ngrep - Network grep

    4:  pv

    5:  dtrx

    6:  dstat - Versatile resource statistics tool

    7:  ffmpeg - Record, convert, stream and play multimedia content

    8:  mtr - Traceroute+ping in a single network diagnostic tool

    9:  multitail - Tail command on steroids

    10: curl - Transfer data and see behind the scenes

    11: netcat - TCP/IP swiss army knife

    12: nmap - Offensive and defensive network security scanner

    13: openssl command line tool

    14: lftp: A better command-line ftp/http/sftp client

    15: Irssi - IRC client

http://www.cyberciti.biz/open-source/best-terminal-applications-for-linux-unix-macosx/