kismet -- Kismet is an 802.11b network sniffer and network dissector.
http://www.kismetwireless.net
Kismet is an 802.11b network sniffer and network dissector. It is
capable of sniffing using most wireless cards, automatic network IP block
detection via UDP, ARP, and DHCP packets, Cisco equipment lists via Cisco
Discovery Protocol, weak cryptographic packet logging, and Ethereal and
tcpdump compatible packet dump files. It also includes the ability to
plot detected networks and estimated network ranges on downloaded maps
or user supplied image files.