tWi-Spy is a USB 2.4 GHz spectrum analyzer ( 2.400 - 2.483 GHz )
WiSpy Tools
WiSPY-Tools are a set of open-source tools for supporting the device. They are known to work on Linux and OSX, and ought to work on BSD variants. The drivers are written as user-space interfaces to LibUSB.
EaKiu - Spectrum analyzer software for OS X that works with the WiSpy
Metrix is now carrying the WiSpy for $99
