NetSpot - NetSpot is a free app for wireless site surveys, Wi-Fi analysis, and troubleshooting
Vistumbler - Vistumbler is a wireless network scanner for Windows Vista and Windows 7. Features:
Wifi Analyzer - Wifi Analyzer is a handy tool which helps you to select a better channel for your wireless router.
NetStumbler - Official source of information about Netstumbler.
WiFi Explorer - WiFi Explorer is a tool to scan, find, and troubleshoot wireless networks.
Wifite - To attack multiple WEP, WPA, and WPS encrypted networks in a row.