http://www.thinkgeek.com/gadgets/electronic/9558/?cpg=ab This new version of Wi-Spy features upgraded hardware and software!
Wi-Spy is the world's smallest 2.4 GHz spectrum analyzer and has been designed specifically for troubleshooting and analyzing Wi-Fi networks. Its software allows recording and playback of data traces and draws pretty graphs.
We're excited about Wi-Spy 2.4x and think you will be, too! The hardware has been redesigned to increase the frequency and amplitude resolution with an added reverse-polarity SMA adapter. Wi-Spy 2.4x is packaged with a powerful little antenna, so it’s good from the start but it's also a snap to screw-on any RP-SMA antenna you choose. The Chanalyzer software has been upgraded to version 2.1, which takes full advantage of the higher resolution with improved graphics and an even friendlier user interface.
Increased frequency and amplitude resolution
Helps you identify wi-fi interference (802.11 b/g/n, microwave ovens, cordless phones, Bluetooth, etc.)
Frequency range is 2.400 - 2.4835 GHz
Record/playback data traces
Frequency/amplitude marker
Frequency / Wi-Fi / Zigbee channel labels
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Spectral, Topographic, and Planar Views
Download Beta version of software for Mac
More details here