i just finished making an arduino fft library
http://wiki.openmusiclabs.com/wiki/ArduinoFFT
it can do anywhere from 16 to 256 points
which returns 8 to 128 real frequency bins
and operates in ~7ms for a 256 point fft
there are multiple output functions
one of which is in octaves
so its pretty useful for doing sound work
Well done!
It compiles with 1.0.1 as well.
What does it mean "there is a pure data patch for visualizing the data." pls?
p.
there should be a pure data patch in the folder
and it plots the fft data on a graph
pure data is an open source graphical programming language
specifically targetted at audio applications
highly reccomended
Isn't "fast Fast Fourier Transform" a tautology? 
i just finished an FHT
which can do the same thing as the FFT
but takes half the time and half the memory
http://wiki.openmusiclabs.com/wiki/ArduinoFHT
it has the same spectrum output options as the ArduinoFFT
so it is probaby preferable for almost all applications