NetStumbler - Detects the access points (APs) of wireless LANs and their SSID, signal strength, signal-to-noise ratio, and other basic information. This program is great to have around to check for possible for interferes, war driving, detecting unauthorized or “rogue” APs, and checking coverage when site surveying.
Wireshark (Formally Ethereal) - Network protocol analyzer that can show raw data packets for Ethernet, Wi-Fi, Bluetooth, and more, depending upon your platform and network adapter.
Kismet – Wireless network sniffer and intrusion detection system. It supports graphical mapping of networks (GPS), hidden network SSID decloaking, detection of known default AP configurations, and more. Plus its client/server architecture allows multiple clients to view a single.
AnalogX PacketMon - Captures IP packets that pass through your network interface, whether originated from the machine or for another PC on the network.
Eric Geier is an author of many wireless networking and computing books including Home Networking All-in-One Desk Reference For Dummies (Wiley 2008) and 100 Things You Need to Know about Upgrading to Windows Vista (Que 2007).