Difficult question, there is so much beautiful music available.
One of my favorite chorale preludes to "Kom heiliger Geist, Herre Gott" is this one, from an anonymus composer (though I suspect it was Johann Michael Bach):
http://partitura.org/index.php/anonymus-komm-heiliger-geist-herre-gott/
Kauffmann wrote a very nice one to the same chorale:
http://partitura.org/index.php/georg-friedrich-kaufmann-komm-heiliger-geist-herre-gott-2/
If you know the chorale for which you'd like some music, you can see if there is something available on my site on this page: http://partitura.org/index.php/genre/choral-prelude/