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

My WIFI Router - Wifi Hotspot creator for Windows

Vistumbler - Vistumbler is a wireless network scanner for Windows Vista and Windows 7. Features:

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...

Kismet - Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system.