The NYT writes, Buttermilk, Often Maligned, Begins to Get Its Due along with a slideshow and recipe, Slate disagrees as to what 'real' buttermilk is.
Featured in the NYT article is Cruze Dairy Farm in Tennessee (a fine buttermilk, I've had it -- in Chattanooga they carry it at Greenlife). My favorite buttermilk is at Wright Dairy in Alexandria AL, but I grew up drinking Barber's with my PawPaw z"l who used to dunk everything from cornbread to saltines in it. Every time I drink buttermilk, I think of sweet PawPaw.
Recipe for my Hallelujah Biscuits (pictured above) here.
University of North Carolina Press last month published 'Buttermilk' by Debbie Moose as part of its new 'Savor the South' series.