Kismet

Kismet will work with any wireless card which supports raw monitoring (rfmon) mode, and (with appropriate hardware) can sniff 802.11b, 802.11a, 802.11g, and 802.11n traffic.

Kismet also supports plugins which allow sniffing other media such as DECT.

Features
802.11b, 802.11g, 802.11a, 802.11n sniffing
Standard PCAP file logging (Wireshark, Tcpdump, etc)
Client/Server modular architecture
Multi-card and channel hopping support
Runtime WEP decoding
Tun/Tap virtual network interface drivers for realtime export of packets
Hidden SSID decloaking
Distributed remote sniffing with Kismet drones
XML logging for integration with other tools
Linux, OSX, Windows, and BSD support (devices and drivers permitting)