This was taken from a previous discussion started by jasonrc with input from userc_2168 and userc_2095 thank you for the input...
We recommend using a USB wireless sniffer from one of the following vendors.
AirPCAP Nx -- works with Wireshark
Good, well-priced, easy-to-use network network analyser
http://www.wireshark.org [Win32 v1.4.14 is stable and works well]
All versions downloadable here: http://wiresharkdownloads.riverbed.com/wireshark/win32/all-versions/
Full featured network analyser
Microsoft Network Monitor 3
A free tool which uses the Wi-Fi card in the laptop/PC.
For doing analysis of the RF/WiFi environment, the following tools are useful:
WiSpy - PC dongle to do 2.4GHz and 5GHz spectrum capture. Can show 802.11 and non-802.11 interference.
inSSIDer - Free scanning tool to show other 802.11 networks within range.
Basic network scans are also available using the wireless utility in your PC or Mac.
Also for RF/WiFi environments if you have an iPad/iPhone/iPod Touch
WiPry - iPhone/iPad/iPod Touch dongle for 2.4GHz analysis
The power meter function is quite handy if you want to make duty cycle measurements or measure actual TX times.
Here is another great tutorial for MACOS users...