How to create simple music visualizer of an iPhone app?
my suggestion is to exploit cocos2d http://www.cocos2d-iphone.org/a very good framework enable developers to easily and quickly realize IOS graphical applications without dealing with OpenGL complexity.
You could for example create small png files representing rows of your FFT bins and animate them according to the music. This would be very easy with cocos2d because it already provides API to load png files and animate them.
bye