Best FFT, Wavelet, and S Transform Algorithms for Real-Time AVR or ARM in C++

Hi friends!
I need a suitable fft algorithm which can be implement on AVR or ARM (preferably AVR) that can be used to take fft from input in real time. (I'm gonna write program using c++)
I also need algorithm for wavelet transform & S transform too.
It would be nice if someone can help me!
Thanks for your help