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
iBwave Wi-Fi - iBwave Wi-Fi software suite brings smart networking solutions to enterprise, education, hospitality, transportation, retail, office, healthcare, public venues, and residential wireless networks.
Kismet - Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system.