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.
TCP Optimizer - SpeedGuide.net - The Broadband Guide. Cable modems, DSL, Wireless, Network security. Free speed tweaks and TCP/IP tools for optimizing system performance.
Ettercap - Ettercap is a suite for man in the middle attacks on LAN.
Throttled Pro - Throttled Pro optimizes your internet connection and provides QoS (Quality of Service) to Mac OS X.
tcpdump - tcpdump is a common packet analyzer that runs under the command line.
Net Speed Booster - Net Speed Booster is an internet speed optimization tool that lets you tweak your internet settings and make them up to the mark.