inSSIDer - inSSIDer Essential makes it easy to maintain small business WiFi.
Wireless Network Watcher - scans your wireless network and displays the list of all computers and devices that are currently connected to your network.
NetSpot - NetSpot is a free app for wireless site surveys, Wi-Fi analysis, and troubleshooting
WifiInfoView - Scans wireless networks in your area and displays extensive information, including: SSID, MAC Address, PHY Type (802.11g or 802.11n), RSSI, Signal Quality, Frequency, Channel Number, and more...
Homedale - With Homedale you can search for Wi-Fi / WLAN Access Points and monitor their signal strength.
My WIFI Router - Wifi Hotspot creator for Windows