Homedale - With Homedale you can search for Wi-Fi / WLAN Access Points and monitor their signal strength.
TamoGraph Site Survey - Wi-Fi site coverage survey and modelling application
Vistumbler - Vistumbler is a wireless network scanner for Windows Vista and Windows 7. Features:
Waircut - Free network audit app
Ekahau Site Survey - Ekahau Site Survey is a flexible wireless site survey software tool that performs automatic wireless coverage calculations and collects detailed information about your wireless network environment.
Kismet - Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system.