inSSIDer - inSSIDer Essential makes it easy to maintain small business WiFi.
Vistumbler - Vistumbler is a wireless network scanner for Windows Vista and Windows 7. Features:
NetSpot - NetSpot is a free app for wireless site surveys, Wi-Fi analysis, and troubleshooting
WiFi Explorer - WiFi Explorer is a tool to scan, find, and troubleshoot wireless networks.
Homedale - With Homedale you can search for Wi-Fi / WLAN Access Points and monitor their signal strength.
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.