Note: this post is from 2006, outbound links may be broken.
Venusian Snail Traffic releases Harmoniac
Harmoniac comes as a VSTi plug-in which works as a synth, and as a VST effect plug-in which has MIDI In to play notes. In this way it can be fed audio to get a natural blowing sound.
Visit Venusian Snail Traffic for links to download Harmoniac VST and VSTi. Sound demos are available as well.