inSSIDer 2 will display all Wi-Fi access points within range and display their MAC address, SSID, RSSI, Channel, Vendor, Encryption, Max Rate and Network Type. Use the filters feature to quickly sort through long lists of access points.
Great news for Linux users! inSSIDer 2, a very popular free/open source Wi-Fi network scanner for Windows Vista and Windows XP is now available for Linux!
Download inSSIDer 2 for Linux (currently alpha) - includes .deb and .rpm files.
Thanks to Kalyh for the tip | Screenshot credits: inSSIDer blog.