tcpdump - tcpdump is a common packet analyzer that runs under the command line.
Vistumbler - Vistumbler is a wireless network scanner for Windows Vista and Windows 7. Features:
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.
inSSIDer - inSSIDer Essential makes it easy to maintain small business WiFi.
Ettercap - Ettercap is a suite for man in the middle attacks on LAN.
Homedale - With Homedale you can search for Wi-Fi / WLAN Access Points and monitor their signal strength.