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
Kismet - Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system.
TamoGraph Site Survey - Wi-Fi site coverage survey and modelling application
Wifi Analyzer - Wifi Analyzer is a handy tool which helps you to select a better channel for your wireless router.
Ekahau HeatMapper - The Free Wi-Fi Coverage Mapping Site Survey Tool